Daniel Radcliffe was initially only offered £125,000 (approximately US $181,500) for this film. The actors' union, Equity, stepped in and negotiated new terms which increased his salary to roughly £2,000,000 (US $3,000,000).
The animatronic Phoenix used to portray Fawkes looked so lifelike (despite the fact that Phoenixes are mythical creatures) that Richard Harris (Albus Dumbledore) thought it was a real living bird when he first saw it.
During production, Emma Watson frequently brought her pet hamster Millie on set. Unfortunately, Millie passed away shortly after shooting began. The set department for the film created a specially-made hamster coffin, complete with velvet lining and the name "Millie" engraved on the top. "I don't think a hamster has ever had a better send-off." Watson said.
On an episode of Have I Got News for You (1990) broadcast around this film's release, the panelists discuss an article claiming that the Russian President (later Premier) Vladimir Putin was deeply disturbed and offended that Dobby the House elf seemed to have been created in his image. There is an undeniable resemblance either way.
The opal necklace, which plays an important role in Harry Potter and the Half-Blood Prince (2009), can briefly be glimpsed inside a display case in Borgin and Burkes' shop in Knockturn Alley when Harry first enters.
The Weasley's car is a Ford Anglia. This is actually the same color and model car that author J.K. Rowling and her best friend from school used to ride around in when they were younger. She used the car for the book, and later the movie, out of her fond memories driving in it.
Many people think that Professor Gilderoy Lockhart is a character based on JK Rowling's ex-husband, but she has said on her official website that Lockhart is based in an egocentric person that she really dislikes, but he is not her ex-husband.
A gag from the book is rendered incomprehensible in the film, due to lack of information. While chatting with the Grangers at the bookshop, Mr. Weasley says, "I understand that other Muggles are afraid of you." This is because they are dentists.
During post-production, 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 the next film, necessitating a recast.
Zoë Wanamaker does not appear in this film as Hogwarts' flying instructor, Madam Hooch, as Wanamaker found the salary unsatisfying. Her character was written out by giving Hooch's speaking lines to McGonagall and other characters.
During the Quidditch Match, some of the music used while Harry and Draco chase the Golden Snitch was used during the speeder chase scene in Star Wars: Attack of the Clones. John Williams did both scores.
On an episode of 8 Out of 10 Cats (2005), Alan Cumming revealed that he had been offered a part in the film, but when he learned from his agent how much more money Rupert Grint, with whom he shares an agent, would be getting paid he refused to sign on as he would not agree to be paid less than a child actor.
A cinema manager in Stavanger, Norway reported that the film was making his younger patrons ill. Evidently many children who had overindulged on sweets and popcorn were throwing up when Ron begins vomiting giant slugs. "It is not a particularly fun task for our employees to have to wash away the sick," he said.
Due to schedule conflicts, John Williams was not able to deliver a fully elaborated score. Composer-arranger William Ross was hired to adapt Williams' material to complete the film's score and was subsequently conducting the orchestra during the recording sessions.
Through advance ticket sales at Odeon cinemas, the film generated more than £1 million (roughly 200,000 tickets) before its release in the UK. An additional £8 million was generated through preview showings at UK cinemas (both Odeon and non-Odeon).
The train station interior used in the film is King's Cross in North London, whereas the exterior shot is actually St. Pancras. The two stations are adjacent to one another, but not the same building. This was done because the architecture of St. Pancras is much more visually appealing.
The trivia items below may give away important plot points.
The script originally said that Hermione would hug Harry and Ron in the final scene. As the then 11-year-old Emma Watson was embarrassed about having to hug the boys in front of the entire cast, Chris Columbus allowed her to change the scene so that Hermione just hugs Harry then starts to hug Ron but the two get embarrassed and resolve to only shake hands. Watson also stated in a recent interview that she kept letting Daniel Radcliffe go too quickly, so the film was "frozen" for a few seconds to make the hug look like it lasted longer than it actually did. Her hesitation with Ron is also taken by fans as a precursor to the relationship that will develop between the two characters.
Foreign language translations had to change Tom Marvolo Riddle's name so that an appropriate anagram could be formed from "I am Lord Voldemort." In Spanish, his name became "Tom Sorvolo Ryddle," which transforms into "Soy Lord Voldemort." In French, his name is "Tom Elvis Jedusor," which becomes "Je suis Voldemort." In Dutch, his name is "Marten Asmodom Vilijn" which is an anagram for "Mijn naam is Voldemort". In Turkish the name is "Tom Marvoldo Riddle" which makes up "Adim Lord Voldemort". In Brazilian Portuguese the name is "Tom Servolo Riddle" which makes up "Eis Lord Voldemort". In Danish, his name is "Romeo G. Detlev Jr." which makes up "Jeg er Voldemort". In Italian his name is "Tom Orvoloson Riddle", which makes up "Son io Lord Voldemort". In Finnish his name is "Tom Gus Mervolo Dolder", which makes up "Ego sum Lord Voldemort".
When Hagrid charges into Dumbledore's office to defend Harry, he is carrying a dead rooster in his hands. This is in reference to a scene in the book (cut from the movie) where Hagrid finds all the roosters dead. The sound of a cock-crow is fatal to a basilisk.
Although the subplot which involved Percy Weasley and Penelope Clearwater (when Ginny discovered them kissing and promised not to tell anybody) was cut, whilst Nearly Headless Nick is on his way to the Great Hall, he does say: "Hello Percy, Ms Clearwater," to the couple as they walk out.