In order to acquaint himself with his three lead actors, director Alfonso Cuarón had each of them write an essay about their characters, from a first-person point of view. Emma Watson, in true Hermione fashion, went a little overboard and wrote a 16-page essay. Daniel Radcliffe wrote a simple one-page summary, and Rupert Grint never even turned his in.
Alfonso Cuarón had the idea to better establish the layout of Hogwarts to make it seem more like a real place and not simply a group of sets. "We started linking spaces," Cuaron said. "You see that there's the Great Hall, and right outside the Great Hall you see a hallway leading you to the staircases. And you take those staircases to the Gryffindor dorm. Or if you walk over the wooden bridge, you exit into a little garden of monoliths. When you go past the monoliths and down this specific path, you get to Hagrid's hut." Essentially the entire layout and structure of Hogwarts and its grounds were altered for this film and remained more or less the same for the following sequels.
Ian McKellen turned down the role of Dumbledore. Having appeared as Gandalf in The Lord of the Rings, he said, "I had enough trouble living up to one legend. Two would be too much to hope for." He also stated it would have been inappropriate to take Richard Harris' role, as the late actor had called McKellen a "dreadful" actor.
Alfonso Cuarón had the idea that when the dementors approached the Hogwarts Express the rain would turn to ice. However, due to his thick Mexican accent the visual effects team misheard "ice" as "eyes". They went as far as to draft a storyboard which depicted eyes falling from the sky, which they presented to a stunned Cuarón, who instantly corrected their mistake.
Alfonso Cuarón had the idea to have Harry, Ron, and Hermione wear everyday clothes more often than their Hogwarts uniforms in order to show more of the characters' personalities. He also gave the rest of the Hogwarts students permission to wear their uniforms any way they wanted to in order to bring a greater sense of realism to the wizards' school, hence why some of the students wear the uniforms very neatly while others have the shirts and ties hanging out.
Originally the script called for Hermione to slap Malfoy as opposed to punching him. During rehearsal for the scene Tom Felton told Emma Watson to slap him, however he had intended for her to not actually hit him, and thus was taken by surprise when Emma smacked him across the face as hard as she could. Emma said she felt terrible about it afterwards and didn't know what she was thinking.
During the filming of the sleeping bag scene, director Alfonso Cuarón, Michael Gambon, and Alan Rickman played a practical joke on Daniel Radcliffe (who had requested to have his sleeping bag next to a girl whom he liked at the time) by hiding a remote-control-operated Whoopee Cushion in his sleeping bag. According to Cuarón, Daniel tried really hard to stay in character while everyone else was laughing.
To make the Knight Bus appear as if it was zipping through traffic at an extremely high speed, the scenes were filmed with the bus driving at normal speed and the rest of the traffic driving at snails pace. The film was advanced though the camera at a slower rate than it would eventually advance on screen. When the scene was played back at normal speed, the bus appears to be driving super fast.
Harry Melling had lost so much weight that the role of Dudley Dursley was almost recast. Eventually it was decided that Melling would continue to play Dudley and would wear a fat suit to make him look heavier.
The bats seen flying around in Hagrid's hut are real. They were particularly challenging to train, and Daniel Radcliffe noted that they tended to urinate everywhere. The animal trainers kept the bats under control using food-rewards; they especially enjoyed banana.
It was Alfonso Cuarón's idea to have a Hogwarts Choir singing as the students enter the school, and he suggested using "Double, Double Toil and Trouble" from William Shakespeare's Macbeth. John Williams agreed, so the tune - and lyrics - ended up being used throughout the film, titled "Double Trouble". The Shakespeare/Macbeth motif was used to the extent of the film being marketed under the tagline "Something wicked this way comes". And, coincident or not, the lines in the play are spoken by witches, who are called the "Weird Sisters". In the novels, the Weird Sisters are a popular wizard band.
When designing the Marauder's Map, graphic designers Miraphora Mina and Eduardo Lima decided to stray from the traditional rolled-up treasure map with burned edges, and designed it instead as a folding map with many layers, each representing a different level of Hogwarts Castle. The shapes of the various areas and objects depicted on the map are defined with written words as opposed to draftsman's lines. The map was printed on white paper and subsequently "aged" using a rich blend of coffee in order to give the appearance of old parchment.
Final Harry Potter film to feature a score composed by John Williams. Williams would continue to be credited throughout the film series for the main motif, "Hedwig's Theme," which was adapted by the composers for the subsequent films. Many fans hoped that Williams would return to compose the music for one of the later films but he ultimately never did.
Chris Columbus originally signed on to direct all of the Harry Potter films. However, he realized that by doing so he would miss out on seeing his children grow up, and decided to pass on directing the third film and subsequent films. He would remain on board for the third film as a producer, but after shooting wrapped he ultimately decided to end his involvement with the Harry Potter franchise.
Gary Oldman says he accepted the role of Sirius Black because he "needed the work". He hadn't acted for over a year, as he had taken time off to be with his family. His last film was Sin (2003), which was filmed in 2002. He also took the role to please his sons. The part made Oldman a hero with them and their schoolmates.
Honeydukes "is floor-to-ceiling psychedelia" and includes Mexican skulls made of sugar. The cast was told that the Honeydukes candy was lacquer-coated, when in fact it wasn't, to prevent candy from disappearing between takes.
J.K. Rowling said she "got goosebumps" when she saw several moments in the film, as they inadvertently referred to events in the final two books, she stated "people are going to look back on the film and think that those were put in deliberately as clues."
Alfonso Cuarón had an idea for there to be tiny people inhabiting Hogwarts, and jumping on piano keys in one scene. J.K. Rowling firmly vetoed it, saying tiny people were completely foreign to the world of her books.
During the Quidditch game between Griffyndor and Hufflepuff, the seeker racing for the Golden Snitch alongside Harry is, in fact, Cedric Diggory. This is unknown to the audience, although readers of the novels will be aware of this fact already. Cedric appears officially in Harry Potter and the Goblet of Fire (2005) (recast as Robert Pattinson).
Some fans were skeptical when Alfonso Cuarón was announced as the director for this film, as his previous film, Y Tu Mamá También (2001), a road comedy about two sexually obsessed teenagers who take an extended road trip with an attractive woman in her thirties, was controversial as much as it was acclaimed, as the film contained explicit nudity and sexuality as well as frequent rude humor. However, David Heyman felt he was the perfect director for the film, as he understood the emotions of teenage boys. Author J.K. Rowling was thrilled when she learned Cuarón would be directing the film, as she had seen and loved "Y tu mamá también" and likewise felt he was an excellent choice for director.
The script for this film makes no mention of Professor Flitwick. Wanting to keep Warwick Davis involved, director Alfonso Cuarón came up with the idea of having him play the choir director. In the next film, Mike Newell liked the look of the choir director and wanted to keep using it. Therefore, the choir director became Flitwick, and his new look has been used for all the subsequent films.
Perhaps the most noticeable difference between this film and the two previous films is the characters' costumes; incoming costume designer Jany Temime (the third costume designer the series has had) gave most of the characters completely new wardrobes, and also re-designed the Hogwarts school uniforms and Quidditch robes. Temime wanted to bring a more modern look to the characters, at the same time being careful not to make them look too trendy. The only character whose outfit did not receive an overhaul was Severus Snape, as Temime thought that the existing billowing black robe suited the character. Temime would end up designing the costumes for all of the subsequent films as well.
Ron's fear of spiders was explained by author J.K. Rowling as stemming from a trauma when he was three years old. In retaliation for Ron's having broken his broom, his brother Fred turned Ron's teddy bear into a spider.
Much of the filming was done in Scotland, so the filmmakers wanted to be sure that a Highland Cow, a breed of cattle native to Scotland, appeared in the film. The large, hairy animal with big horns can be seen in front of a shop in Hogsmeade when Ron and Hermione go and look for Harry after he leaves the pub.
Despite his initial reluctance to accept the role of Albus Dumbledore, Richard Harris, who portrayed Dumbledore in the first two films, was determined to portray the character through the entire series. However, following the filming of Harry Potter and the Chamber of Secrets (2002) Harris was diagnosed with Hodgekin's lymphoma. During post-production on that film, producer David Heyman went to visit Richard Harris in the hospital. Though he was very weak from his illness, Harris insisted that the role of Dumbledore not be recast. Sadly, Harris passed away shortly before production was to begin on Prisoner of Azkaban, necessitating a recast.
Alfonso Cuaron is known for his use of lengthy shots and restlessly moving cameras. Upon accepting the role of director for this film he was advised by his close friend, fellow Mexican director Guillermo del Toro, to tone down his more eccentric film-making techniques and instead be faithful to the previous two films.
When the Marauder's Map is opened for the first time, the name 'Newt Scamander' can be seen. This was simply meant as an Easter Egg: in the Harry Potter universe, Scamander wrote the book "Fantastic Beasts and Where To Find Them" that is mandatory reading at Hogwarts, but he isn't a teacher there. Scamander eventually got his own movie with Fantastic Beasts and Where to Find Them (2016), where it is revealed that he is friends with Albus Dumbledore, so in 'Prisoner of Azkaban', he may be simply visiting.
Shooting for the Knight Bus sequence took place on the streets of Palmers Green, North London. The film crew and local police gave the spectators strict instructions to keep back during filming and not to use flash photography or it would ruin the take. Despite these warnings, there were still people who took pictures of the scene with flash, and at one point a driver ignored the police and the 'No Entry' and 'Diversion' signs and nearly drove into the oncoming traffic.
Costume designer Jany Temime wanted to establish a color scheme for the outfits of each the three main characters to further define the characters' personalities. Harry's clothes consisted of neutral colors such as grey, white and black, as she felt Harry wasn't entirely comfortable in his skin and therefore would not wear bright colors. Ron's clothes consisted of warmer tones such as brown, orange, and red, reflecting the fact that his mother used to knit sweaters for him and the style still is in him. Hermione's color scheme, consisting of blue, pink, and beige, was meant to balance out Harry's and Ron's colors and also to show a bit of Hermione's feminine side.
The scene where Professor Lupin teaches Harry the Patronus Charm to defend against the dementors was filmed on the set that served as Dumbledore's office in Harry Potter and the Chamber of Secrets (2002). Alfonso Cuaron liked the set and wanted to use it in this film. Since the book makes no mention of Dumbledore's office, the set was instead re-decorated as a different room entirely (referred to as the Astronomy Room in the script). It was reverted back into Dumbledore's office for Harry Potter and the Goblet of Fire (2005) and subsequent films.
Illusionist Paul Kieve served as a consultant. He taught magic to several members of the cast including Daniel Radcliffe and Emma Watson (Harry and Hermione) and worked extensively to create physical magical effects. He is the only professional illusionist to have worked on any of the series of films, and as a result, this film includes a number of discrete, authentic practical illusions throughout. The 2-Disc DVD even turns finding them into a game for the viewer. Kieve also makes a cameo appearance in the film, during the Three Broomsticks pub scene.
The rickety wooden bridge connecting Hogwarts to the surrounding landscape was going to be created entirely in the studio, backed by a green screen. This would enable the filmmakers to add a background digitally in post-production. While a few scenes were filmed in the studio, Alfonso Cuarón decided to film the scene where Harry talks to Professor Lupin about his parents on location in Scotland. A section of the bridge was constructed in the Highlands for the shoot, and even though it was a lot sturdier than in appeared, the extremely heavy winds proved to be a challenge.
Not only may Professor Remus Lupin's last name possibly refer to a wolf ("lupus" being the species name of the wolf), but his first name does as well. In Roman mythology, Romulus and Remus were the founders of Rome and were both raised by a female wolf. (In actuality, Lupin is a type of flower, and Remus actually translates to "swift".)
Although the Dark Lord himself does not appear in the movie, a moving painting of him can be seen in the lower right hand corner of the screen when Harry and his friends walk up the stairs to discover the Fat Lady singing.
Two Persian red cats were used for the role of Crookshanks: Crackerjack and Pumpkin. The trainers saved the cats' shed fur, rolled it into balls, and clipped these onto the cats in order to achieve Crookshanks's mangy appearance.
During the scene where Buckbeak the Hippogriff is introduced, just after Ron pushes Harry forward there is a shot of the animal pooping. The CGI team believes this might be the first example of a CGI animal doing this, but the BBC miniseries Walking with Dinosaurs (1999) had done it first. This *is*, however, the first time such a scene is done for a feature film.
The character of Gregory Goyle, while appearing in a few scenes, is largely absent from the film. This was due to actor Josh Herdman injuring his arm and being unable to film certain scenes. Actor Bronson Webb was cast as an unnamed Slytherin boy (referred to as "Pike" in the script) who filled Goyle's role in those scenes.
In the opening sequence, Harry is seen practising a spell. According to the wizarding laws, it is illegal for anyone under the age of seventeen to perform magic outside of Hogwarts. This law was an important plot point in two other Harry Potter movies/books: Chamber of Secrets, where Harry receives a warning after Dobby uses magic in the Dursley's house and Order of the Phoenix, where Harry is summoned for a disciplinary hearing after performing a Patronus charm.
Although the stone circle seen in the Hogwarts Grounds was a creation of the filmmakers, it was based upon actual stone circles found throughout Britain (e.g. Stonehenge). The stones were created at Leavesden and were delivered by helicopter to Glencoe, Scotland, where they were set into holes dug into the ground. They looked so realistic that the young actors ultimately asked director Alfonso Cuarón if the stones were the reason why he picked that particular location. "It's always gratifying when your work is mistaken for the real thing!" said art director Alan Gilmore.
The effects team spent six months creating the dementors. Originally, Alfonso Cuarón wasn't thrilled with the idea of using CGI and wanted to use more traditional techniques such as puppetry. The filmmakers tried a basic technique with a dementor puppet floating in the breeze but weren't satisfied with the way it looked. Puppeteer Basil Twist showed them a technique that involved putting the puppet in water and shooting it in slow motion with the film reversed. The filmmakers liked the way it looked but realized that this would be an impossible task, so in the end they decided to use CGI to create the dementors.
Production designer Stuart Craig has revealed that the appearance and location of Hagrid's Hut as seen in this film and subsequent films was closer to his original design for the hut, which had been compromised for the first two films due to the scenes being filmed in a small patch of land outside the studio, rather than on location in Scotland.
After the death of Richard Harris, many actors were considered for the vacant role of Albus Dumbledore. Christopher Lee was in the frame for a while, and there was a rumor (reported in many newspapers) that Ian McKellen was also considered. The Harris family wanted Richard's longtime friend and peer Peter O'Toole for the role but there were studio concerns over insuring O'Toole for the remaining five films. Richard Attenborough also lobbied for the role but was ultimately turned down.
Among the difficulties associated with filming in Scotland was the amount of rain that fell during the shoot. During the breaks in filming, helicopters delivered large bags of gravel to the set in order to prevent it from washing out. Many of the filmmakers were concerned as to how this would affect the look of the film, although director Alfonso Cuarón and cinematographer Michael Seresin insisted that it was the best look that they could have come up with.
The rating in the Netherlands for this film is "not under 9". This rating was created especially for the film, since it was judged to be too scary for 6 year olds and the next rating, "not under 12", would exclude too much of the target audience.
The film was offered to director Guillermo del Toro but he opted to do Hellboy (2004) instead. Del Toro was good friends with Alfonso Cuarón and when he learned that Cuaron had been offered the role of director he passionately encouraged Cuaron to take the job.
Subplot involving the Sneakoscope concept from the novel, as well as an attempted attack on Ron in his sleep at Hogwarts by Sirius Black, were filmed (and can be partially found as additional scenes on some DVD versions) but ultimately scrapped from the finished version. Oddly enough, a small bit from the latter, Harry's lines about missing a chance to capture Black, was still featured prominently in most promotional trailers. (Source: 2-Disc DVD extras & trailers).
David Thewlis was Alfonso Cuarón's first choice for the role of Professor Lupin. He accepted the role on advice from Ian Hart, the man who was cast as Quirrell, who told him that Professor Lupin was "the best part in the book."
In the scene where Harry is given the Marauder's Map by the Weasley twins, the name "Moony" is misspelled as "Mooney". While not really a mistake, there is still an interesting connection. The film's visual effects supervisor is named Karl Mooney. The spelling was changed deliberately for the in-joke.
Two Knight Buses were built: one for exterior shots and one for interior shots. The exterior of the bus was created by taking an ordinary double-decker London bus, adding a level, and painting it purple.
J.K. Rowling allowed Alfonso Cuarón to make minor changes to the book, on the condition that he stuck to the book's spirit. She allowed him to place a sundial on Hogwarts' grounds, but rejected a graveyard, as that would play an important part in the then unreleased sixth book.
This film actually marks the second time that Michael Gambon has replaced Richard Harris. Harris had previously played Inspector Jules Maigret in Maigret (1988), while Gambon took over the role in the television series Maigret (1992).
The geometric staircase at St. Paul's Cathedral, London, was used as the staircase that leads to the Divination classroom. It was the only indoor area of Hogwarts shown in this film to utilize an actual location for filming, as opposed to a studio set. The first film made heavy use of the various castles and cathedrals around Britain for much of the areas of Hogwarts, with additional sets being built for the second film.
The design of the large clock which functions as a visual motif in this film appears to be based on the Old Town Clock (also called the "Orloj" - pronounced "OR-LOY") in Prague, Czech Republic. The Orloj tells not only the time, but shows the month, the sign of the Zodiac, and shows the relative positions of the moon and sun.
Sir Cadogan, played by Paul Whitehouse, was cut almost completely out of the film. You do still see Sir Cadogan jumping through several paintings behind Ron, Harry and Hermione during the Fat Lady's disappearance.
The crows seen in the latter part of the film are African Pied Crows. They were raised in captivity in California, as crows bred in captivity were easier to train than wild crows. The crows typically can be found throughout Africa.
David Thewlis had seen the first two films and had only read part of the first book, although after taking the role he read the third. He was excited about the prospect of making a children's film, and thoroughly enjoyed filming.
At the time of its release, "Harry Potter and the Prisoner of Azkaban" was the shortest of the Harry Potter films, despite the fact that the book was longer than both the previous books. After all eight films were released "Prisoner of Azkaban" ended up being the third shortest film in the series, behind Harry Potter and the Deathly Hallows: Part 2 (2011) and Harry Potter and the Order of the Phoenix (2007), the latter of which is based on the longest book in the series.
Some dubbed versions retain a voice likeness of the late Richard Harris for the character of Dumbledore, despite there being a quite different person in the role on screen. The Icelandic dub is one such case.
Hogwarts grew and expanded significantly with the third film. For the first time, the Hogwarts courtyard and bridge were seen. At the end of the bridge, rock monoliths were placed onto the hillside to evoke a Celtic feeling. The use of live-action also significantly changed the look of Hagrid's hut. In the first two films, it appeared at the end of a flat stretch, right in front of the Forbidden Forest. The third film utilized the more rugged Scottish locations to place Hagrid's hut at the bottom of a steep hillside. A large pumpkin patch was added behind the hut.
The Dursleys have three television sets in their house; one in the living room, one near the dining table, and one in the sunroom. While not mentioned in the film, it is explained in the book that Dudley complains about the long walk from the fridge to the television in the living room.
The reason for this installment of the Harry Potter series being so distinct from the original two is the influence of its director, Alfonso Cuarón, whose trademark directional style is noticeable throughout: the majority of shots are filmed on a handheld camera which gives a naturalistic style to many scenes, several shots are held for a longer than usual time without cutting, and there is a generally washed-out and darker color pallet. All of these traits are especially noticeable in Cuarón's next film, Children of Men (2006).
The German subsidary of Warner Bros. tried to cut down the film (as they did with Harry Potter and the Chamber of Secrets (2002)) to secure a more commercial "Not under 6" rating. They submitted several versions but all were rejected by the German ratings board FSK for this rating. In the end the uncut version was released with a "Not under 12" rating.
Chris Columbus, the director of the first two Harry Potter films and producer of this one was amazed how beautifully Daniel Radcliffe, Emma Watson and Rupert Grint matured over the series, as compared to some child actors who lose their charm, or fail to develop into good adult actors, as they age.
The Shrieking Shack actually moves. During the scene where Lupin and Sirius reveal the truth about James and Lily's death to the others, the doors are moving. If you look closely, the walls are actually swaying from side to side causing the doors to move as well and accounts for the wood's creaking and groaning. It gives the illusion that the building is only one strong wind gust from being blown over and simply makes it all the creepier.
Alfonso Cuarón originally wanted to move away from CGI toward puppetry. He hired master underwater puppeteer Basil Twist to help, using puppets to study the potential movement of the Dementors. Once it became apparent that puppetry would be too expensive and unable to portray the specific elements of the Dementors, Cuarón turned to CGI; however, he and his team did use footage of Dementor puppets underwater as a basis for the flowing movements of the computer-generated Dementors.
In the books, a Patronus charm is used as a shield from a Dementor, constructed of a powerfully happy memory or feeling, and the Dementors feed on that rather than on the person. In the movie however, it is used mostly as, what seems to be, a Dementor repellent.
In order to reduce the number of scenes that would ultimately end up on the cutting room floor, screenwriter Steve Kloves and director Alfonso Cuarón carefully decided which scenes from the book were essential to the plot, and which could be written out.
In the scene where Harry is shown getting down from the Knight Bus and entering the Leaky Cauldron a wizard sitting inside and stirring his mug by magic is shown reading "A Brief History of Time" by Stephen Hawking.
When producer Chris Columbus scripted Young Sherlock Holmes (1985) it foreshadowed his future association with the Harry Potter series; the teenage Watson resembles Harry Potter; school experiments; Holmes has a rivalry with a fellow student, Dudley very much like Harry's with Draco Malfoy; Dudley and Malfoy both come from rich parents; cavernous libraries; sweets; train stations; the novelization uses the word potty/Potter; students being injured and needing to see the school nurse; teachers and students eating in the Great Hall; Holmes, Watson and a third character Elizabeth solving mysteries at school while Harry, Ron and Hermione do the same at Hogwarts; staircases; Harry/Holmes and Watson creeping through a school library at night; both Watson and Hagrid say "sorry about that"; the end of school term; the threat of expulsion; no family for Harry to return to, even at Christmas; Harry has a scar on his forehead while Holmes has one on his cheek; seemingly innocent teaching staff exposed as the opposite; head boys, etc.
Before the Weasley twins gave Harry the Marauders Map, you could see his footprints in the snow, despite the fact that Harry was wearing the invisibility cloak. In a later scene, when Draco Malfoy was about to fight Ron, Draco gets hit by a snowball and is then seen to be messed with by Harry under his invisibility cloak, yet you see no footprints being made in the snow by him.
The scene at Hogwarts includes a chorale of part of the witches chant from William Shakespeare's Scottish play Act 4. Outlander (2014) By the Pricking of My Thumbs (#1.10) is directly from the chant/play.
According to J.K. Rowling, Sirius is the oldest of the Marauders, with a given birth date: 3 November 1959. While Peter is not revealed, based on the fact, James is the youngest (the grave stone in Deathly Hallows reveals that he was born in March 1960).
When Chris Columbus scripted Young Sherlock Holmes (1985), Watson believed Holmes obsessed over a case, even at Christmas because unlike other boys his age, he had no family to go home to, like Harry Potter or Kevin McCallister, and Columbus has ties to both the Harry Potter and Home Alone franchises.
Caio Cesar, a prominent Brazilian voice actor who dubbed Daniel Radcliffe as Harry Potter and in other films, was also a military cop and passed away aged 27 in 2015, after being shot in his neck at the Complexo do Alemão slums, in Rio de Janeiro.
Ian Brown: the singer (formerly of The Stone Roses) appears briefly in the bar at the start of the movie reading "A Brief History of Time" by Stephen Hawking. He was originally cast as the pub landlord, but the role was cut right down due to timing issues.
Alfonso Cuarón: [Use of wide-angle lenses] The film was shot entirely on wide-angle lenses, ranging between 14-24mm. Cuaron insisted on the wide-angles because he wanted to let the audience see both the foreground and the background at the same time.
Alfonso Cuarón: [Mexico] References to director Cuarón's Mexican nationality abound. On the fountain in the courtyard in front of the clock tower, there are several statues of eagles eating snakes, as on the National Seal of Mexico. Also, among the many sweets offered at Honeydukes are skulls made of sugar, known as Calaveras, which are a popular treat in Mexico on "El Dia de los Muertos," or the Day of the Dead. And, after Dumbledore says his final lines outside the infirmary, he goes down the stairs humming "La Raspa", the Mexican Hat Dance.
The trivia items below may give away important plot points.
Azkaban Prison, though mentioned, never actually appears in the film. Nonetheless, concept art was created by both conceptual artist Andrew Williamson and production designer Stuart Craig. Both sketches depict Azkaban as a triangular stone fortress built on the edge of a giant waterfall. When Azkaban is seen for the first time in Harry Potter and the Order of the Phoenix (2007) the filmmakers looked to these sketches and ultimately decided to keep the triangular design but relocated the prison to an island in the middle of the ocean (closer to how it was described in the book).
Early in the film, Harry sees a newspaper article with a photograph of the Weasley family in Egypt. Though it is never again mentioned, this is a very important plot point in the book. While on an inspection of Azkaban the Minister of Magic had a copy of that paper, and gave it to Sirius Black who recognized Peter Pettigrew disguised as Scabbers. This is what made him decide to break out of Azkaban, track down Scabbers at Hogwarts, and take his revenge by killing him.
Although the Marauders' Map, created by Messrs Moony, Padfoot, Prongs, and Wormtail plays a large part in the film, the identities of the first three are not made clear. This is surprising as this was important to understanding this plot in the book. Moony was Lupin, who was supported by his three friends. These learned "Animagus" shape shifting techniques to sympathize with him. James Potter was Prongs the Stag (a trait passed on to the Patronus of his son Harry), Sirius Black was Padfoot the Dog, and Peter Pettigrew was, more obviously, Wormtail the Rat.
The only film in the series where Voldemort does not appear in some form. It is often stated that he also doesn't appear in Harry Potter and the Half-Blood Prince (2009), and while this is technically true, Tom Riddle appears during flashback sequences.
Lupin says that he was very close with Harry's mother. This may seem at odds with the book's story that Lily Evans was a close friend of Lupin's rival Severus Snape. However, J.K. Rowling revealed that after graduating from Hogwarts, Lupin still found it difficult to find paying work, because nobody wanted to employ a werewolf. James and Lily, therefore, financially supported him.
The filmmakers wanted to stray away from the traditional werewolf and instead portray Lupin's lycanthropy as a debilitating disease. Hence, Lupin in his werewolf form is depicted as emaciated and mostly hairless, making him appear both frightening and pitiful.
Professor Dumbledore seemingly stalls the executioner by saying that he needs to sign the execution order, and that he has "a very long name". In Harry Potter and the Order of the Phoenix (2007), his full name is revealed to be Albus Percival Wulfric Brian Dumbledore.
Ron's dream about spiders making him tap-dance is a two-in-one reference of the next book. In 'Goblet of Fire' there is an unforgivable curse where you can control what someone does, taught by Professor Moody. He makes a spider tap-dance on the desk.
The ending of the film, in which Sirius escapes on Hagrid's hippogriff, is actually a reversal of the opening of Harry Potter and the Sorcerer's Stone (2001), in which Hagrid arrives on a flying motorcycle which, the book reveals, he borrowed from Sirius.
Despite featuring the idea of a mass murder as the back story, this is *arguably* the only book/movie in the series where no person dies in the story itself. The argument is that, while the villain in Harry Potter and the Chamber of Secrets (2002) was destroyed, he was a manifestation of Voldemort's hocrux, and can be said never to have been alive to begin with.
The executioner sent to kill Buckbeak is actually Walden Macnair, who is later revealed in the graveyard scene in "Harry Potter and the Goblet of Fire" to be one of Voldemort's first Death Eaters. It was explained later by Hagrid that Macnair was sent to the Giants to try and recruit them for Voldemort (which is why Dumbledore sent Hagrid to talk to them in the beginning of "Harry Potter and the Order of the Phoenix" - to keep them from claiming loyalty to Voldemort).
Ron's prediction for Harry during divination class -- that he would suffer but be happy about it -- actually rings true by the end of the movie. He suffers through the "knowledge" that Sirius killed his parents, only to find that this isn't true, and, in fact, Sirius can offer Harry a loving home.
Clocks and time are a major motif in this film. In addition to the large clock tower at Hogwarts there are other clocks that chime at various points in the film when an important event takes place, such as the cuckoo clock in the Dursleys' house which goes off when Harry blows up Aunt Marge, and the grandfather clock in the Hogsmeade tavern which chimes right when Harry learns that Sirius Black is his godfather.
There is a clue in the opening credits about Sirius Black. In the very beginning where they show the Warner brothers logo you see a tiny glow then you hear a dog barking then the camera slowly zooms in and the light glows again and your hear a dog bark again. Every time there is a glow it's followed by a dog barking outside. You see that the glow is from Harry's room as he is practicing his lumos maxima spell.He doesn't notice it of course because he is inside his room practicing, but it's Sirius. He was the one barking EVERYTIME Harry was doing his spell. He was there watching Harry before the story started!