Martin Freeman and the Elvish actors all play characters who cannot grow facial hair. The actors, however, not only grew facial hair, but had a complete five o'clock shadow by the end of a day's filming, even if they were clean-shaved at the beginning of the day. This shadow appears blue on film. Rather than shave repeatedly during the day, the actors had orange make-up applied, which canceled out the blue shadow.
During filming, Ian McKellen had to spend hours in a box with nothing but a microphone and pictures of the dwarves for company (the footage would be edited in to make him look taller than the dwarves), and was so upset by this that he exclaimed "This is not why I became an actor!" The microphone was still on and everyone on set heard him as a result. In consolation, the cast and crew surprised him by sticking gifts and encouragement messages into his trailer.
Bilbo steals the keys to the prison from an Elf addressed as Elros. Elros is also the name of Elrond's brother. The two brothers had both human and Elvish ancestry on both their mother's and father's side, and as such were perfectly half-Elf and half-Man. While Elrond chose to be an immortal Elf, Elros chose to become a mortal man. He thus became the progenitor of the Numenorian race, and an ancestor of Aragorn.
Gloin takes great insult that the portrait of his bearded wife is mistaken for being his brother. In the extended edition of The Lord of the Rings: The Two Towers (2002), his son Gimli notes that Dwarf women are often mistaken for men, on account of their beards.
The sudden scars on Thranduil's face are a creation of the film adaptation. However, his scars may reflect a little-emphasized facet of J.R.R. Tolkien's lore: elves' "Fëa" (a metaphysical concept analogous translatable as "soul") occasionally influences the "Hröa" (the fleshly, physical body), particularly under moments of extreme stress. This can manifest as extreme physical changes that reflect the mind's state, in this case deep war scars. This is in accordance to J.R.R. Tolkien's texts and books, the last battle where Thranduil fought was the Last Alliance at the end of the Second Age (about 3000 years earlier), where Sauron was defeated.
The fish that were dumped into the barrels to hide Bilbo and the dwarves were real fish with a few rubber props mixed in. At one point Adam Brown (Ori) had as much as 400 pounds of fish dumped directly on him. Brown hates fish and had to fight his own phobia while buried in them in the barrel and while he waited for crew members to pull them off of him. Since the fish were slippery, they had to be taken out by hand one at a time.
The Mirkwood scenes required nearly all color to be drained from the footage, in order to make the forest appear "sick". As a result, objects that needed to retain their color, such as certain mushrooms and lichens, had to be painted in neon colors to be noticeable at all in the final film. Peter Jackson remarked that the set looked like it was painted in 1967. The actors also had to have their faces painted unusually red in order to retain color.
Benedict Cumberbatch studied iguanas and Komodo dragons at the London Zoo's Reptilian House to prepare for the voice of Smaug, aiming for a tone that would "bridge between animal and human, a deep and rasping guttural dryness to the voice."
It took one processor-week to render a scale from Smaug's body. In other words, if a single computer processor were used, each scale would have taken a week to render. Fortunately, Weta Digital used a large server farm of multi-processor machines for its effects rendering.
After the barrel riding sequence, as the Orcs continue to search for the Dwarves, one of them dips his finger into a pool of blood on the ground and tastes it, spitting in disgust and says "Dwarf blood!". This mimics a scene from The Lord of the Rings: The Two Towers (2002) where Gimli dips his finger in a similar fashion into some blood left on some leaves and tastes it, only to spit out in disgust and say "Orc blood!"
Aside from providing the voice of Smaug, Benedict Cumberbatch also supplied motion-capture performance to portray the dragon. However, since Smaug's body is impossible to motion-capture fully, only Cumberbatch's face, upper body and arms were captured and the rest of the body was completed in keyframe animation.
While the cast was shooting the barrel escape scenes in the specially-constructed indoor "rapids" tank, several of them (without naming names) stated that they had to "relieve" themselves in the water, since they had to stay in the tank for so long without so much as a lunch break. When Martin Freeman found out, he was furious, since Bilbo spends all of his time during that scene directly in the water, and had been swallowing a great deal of it.
Several of the women who turn out to see Bilbo and the dwarves leave Lake Town for Erebor are actually tall male crew members who were dressed up as women to get the proper scale of humans vs dwarves & Bilbo for the shot.
The stone that Kili carries is called Labradorite, named after Labrador, Canada, where it was discovered. The Inuit people call it the "frozen fire of the Aurora Borealis" and it is considered to be magical, which may be the reason why Kili jokes about what may happen if anyone were to touch it. Labradorite can appear black, gray-green, dark gray or grayish white and refracts colors such as blue, green, gold and red in the light. You see these qualities as Tauriel inspects the stone herself.
This is the only movie in the Middle Earth series directed by Peter Jackson to not feature Frodo and Gollum. It is also the first of the many Middle Earth films, including animated ones, not to feature Elrond. This leaves Gandalf and Galadriel as the only ones to appear in every single film based on Middle Earth series written by J.R.R. Tolkien, as Bilbo doesn't appear in The Lord of the Rings: The Two Towers (2002).
The 48 FPS 3D movie was shipped to some theaters via a standard SATA hard drive. It was shipped with a security code that prevented the content from being viewed or copied until the code was released by the distributor about 24 hours in advance of the initial release time of the movie. The 48 fps 3D version of the movie occupied 639 GB of data on the SATA hard drive. The theater in question could have downloaded the entire movie via a secure satellite link, but the download would have taken more than a full 24 hours. Given that 96 frames per second are required for the 3D picture (48 fps for each eye), the data size for each frame for each eye is about .66 megabytes.
Peter Jackson admits he misread the text when depicting the Eye of Sauron in the Lord of the Rings films. Sauron's appearance in this film, as a black apparition forming the pupil of the Eye, is much closer to Tolkien's descriptions.
The romance between Kili and Tauriel was always intended to be in the film from as early as 2010 with her relationship with Legolas being strictly platonic. But when re-shoots were done to turn it into three films, the studio forced them to write Legolas into the love story and turn it into a love triangle. Both Evangeline Lilly and Peter Jackson have admitted they hated the idea of a love triangle and just wanted to tell a simple love story.
While the novel and the previous film The Hobbit: An Unexpected Journey (2012) are mostly told through Bilbo's point of view, this film shifts the perspective to mainly Gandalf and Thorin with little involvement from Bilbo in many major scenes.
This is the only Peter Jackson-adapted J.R.R. Tolkien film that does not include a "Wilhelm Scream", something that has become a trademark for him. In November 2014 the extended edition included two scenes in which the "Wilhelm Scream" is used.
Robert Kazinsky was cast as Fili and had filmed a few scenes, but left the project and returned to England about a month after filming started due to personal reasons. He was replaced by Dean O'Gorman.
When Bilbo is examining the Ring, Black Speech is heard as the scene segues to Dol Guldur; it is the end of spell that Sauron inscribed on it when the Ring was forged: "One Ring to rule them all, and in the darkness bind them."
The sound editors for The Desolation of Smaug pulled an all-nighter to finish the sound before handing it in, because they were behind schedule due to the sudden change of plans from two movies to three movies.
In the original screenplay, Bofur was supposed to be part of the group that accompanies Thorin and Bilbo to the Lonely Mountain. However, James Nesbitt had to return to the UK to work on another project, so the script was rewritten to accommodate his schedule.
In the "Barrels out of Bond" sequence, there are two instances where Thorin throws a sword at an orc to kill them, first to protect Balin when an orc jumps at him from above, and second to stop an orc from attacking Legolas from behind. If you pause the film at these times you can see that in both instances the sword he throws has the same design as Balin's sword, which he used in both films until was taken by the Wood Elves upon their capture in the forest.
It was decided to CGI Azog, Bolg, and the orcs, with the decision with Bolg being made so suddenly that whole sequences had to be re-shot, which is why in the trailers Azog is the one chasing the dwarves but in the film it's Bolg.
Saoirse Ronan was offered the role of another wood-elf named Itaril (which may or may not have been Tauriel's original name) but she turned it down because she felt she couldn't commit to such a long shoot.
Most notably, Smaug was apparently a four-legged western dragon in the first film, but to follow the description in the book, referring to him as a "wyrm", he was redesigned to be a more snake or bird-like wyvern-type dragon in the second film. In the Blu-ray extended edition of the first movie, his forelimbs were changed to winged arms. Many other parts of his body have also been altered from what he looked like in the first movie.
Stephen Colbert: as the eyepatch-wearing Lakewood Spy who knocks on the door with the walking stick. Colbert, a longtime Tolkien fan and expert, had brought his wife and two of his sons to the shoot. When his scene was completed, Peter Jackson personally presented Colbert with a replica of the sword Sting.
Peter Jackson: at the beginning of the film as the camera sweeps through the town of Bree, he walks out of the pub looking drunk and eats a carrot. He previously had a similar cameo in The Lord of the Rings: The Fellowship of the Ring (2001). Jackson also filmed another cameo for this film; he played another spy in Lake Town, a man who'd hide in a basket and signal his comrades with wild bird calls. The scene was adamantly vetoed by his co-producer and -writer, Philippa Boyens and was never used.
The trivia items below may give away important plot points.
According to Kili, the Labradorite stone he carries was a gift from his mother to remind him of his promise to return to her. When he is looking at it in Thranduil's dungeons, runes can be seen on it. They translate to "inikhde", a word in Khuzdul (the dwarvish language, created by J.R.R. Tolkien) that means "return to me".
The only time Legolas blinks is when he realizes he has been wounded. This is in keeping with the character, as the only time Legolas blinks in the Lord of the Rings trilogy is when he is strongly surprised.
Thranduil makes it clear that he doesn't consider Tauriel to be worthy of his son Legolas, but the film avoids explaining why. In the books, it is established that the wood-elves of Mirkwood are Silvan, but Thranduil and his family are Sindar ('Grey Elves'), a more noble ruling class of elves. This difference is also alluded to in the film by the fact that Thranduil and Legolas are blonde, while all the other Mirkwood elves have darker hair (although Legolas' hair colour was never declared in the books).
When Bilbo first confronts the dragon Smaug, he explains who he is in various nicknames. He says that he comes from "under hill" to which Smaug replies, "Underhill?". This is the name by which Frodo Baggins covered his true identity "The Lord of the Rings" as per Gandalf's request.
When Kili is being saved by Tauriel from the Morgul-tipped arrow, Kili sees Tauriel surrounded by light. In The Lord of the Rings: The Fellowship of the Ring (2001), the first time that Frodo, similarly hurt by a Morgul knife, sees Arwen, she also appears surrounded by light.
There is a fan theory that the Arkenstone is actually one of the lost Silmarils, from J.R.R. Tolkiens "The Silmarilion." Changes in the visual design of the Arkenstone from how it is described in the book seem to indicate Peter Jackson (or one of his design team) subscribe to that theory. Since they do not have film rights to that book, explicit references to its story and characters do not feature in the movies.
Richard Armitage hated the tan overcoat he was given to wear when the Company traveled from Laketown to Erebor, and begged Peter Jackson to find a way to have him somehow lose it. Jackson then wrote the scene in which Smaug lets a blast of fire loose on the Company, catching the back of Thorin's coat on fire and necessitating its removal.
In order to keep Kili's bodily proportions correct while filming the scene in which Tauriel is healing his leg wound, Aidan Turner's upper body and his scale double's legs were filmed performing the same scene with the cast twice, then spliced together in post-production.
When Legolas fights against Bolg and the rest of Orcs in Laketown, he uses Thorin's sword ("Orcrist", the Goblin-cleaver), which he kept after disarming Thorin and the Dwarf company when they were captured in Mirkwood.
When Bilbo fights against a giant spider in Mirkwood with his sword, he hears the spider say "It stings, it stings". This gives the name to Bilbo's sword, which years later he would give to Frodo in The Lord of the Rings: The Fellowship of the Ring (2001).
The first meeting between Gandalf and Radagast takes place in the mountains of High Fells of Rhudaur, to investigate an underground cave. They find some tombs desecrated, and its iron doors blown out. These are the tombs of the Nazgul (the ancient nine kings of men), mentioned by Galadriel (Cate Blanchett) in The Hobbit: An Unexpected Journey (2012). Rhudaur is a Sindarin word (a fictional language created by Tolkien) and means "Eastern Forest".
The scene where the group tries to bury Smaug in gold in the forges was added only because the filmmakers needed a cliffhanger (they confirmed this when asked) and the actors and some of the crew literally had no idea what they were filming until they saw the completed film.
The dwarves' capture by the giant spiders and the elves of Mirkwood is considerably different from the book. In the book, Bilbo lures the spiders away with a song, and once the Company has escaped, Bilbo and the dwarves chase firelight into open spaces to get to the elves. Each time, the fire is snuffed out. This happens three times before the dwarves are captured and imprisoned in Thranduil's dungeons.
In the original script, Tauriel healed one of Bard's daughters (most likely Tilda) but when re-shoots happened it was changed to Kili, which coupled with the aforementioned Bolg switch suddenly explains Kili being hit with an arrow.
Tolkien was strongly inspired by Scandinavian languages and mythology (Norse mythology). The names of various characters are sometimes from the mythology other times they simply reflect the character itself. When we meet Beorn for the first time he is in the shape of a bear. Björn/Bjørn is pronounced very similarly, is a scandinavian name and means bear. Later a voice is heard whispering "Attercop", (edderkop) meaning spider.