Awesome, Dear Boy: David Thewlis took the role of Lupin after Ian Hart assured him it was "the best part in the book" and because he was excited to make a children's film. He reportedly enjoyed filming very much.
B-Team Sequel: Chris Columbus stepped down as director due to family commitments. He stayed on as producer for this film, and then vacated the series.
This trope never gets more averted in the series than it is in this movie. Hogwarts is meant to be located in Scotland, but for the most part, the Potter films were done in England with only background plates shot in Scotland. For Azkaban, however, they actually took the principal cast on location to Scotland, where they filmed the scenes involving Hagrid's Hut at Clachaig Gully in Glencoe. That said, some of the exteriors were still done in England, particularly at Virginia Water in Surrey.
Between having the pre-existing sets from the first two films and the fact that the characters spend a lot more time outdoors in this one, Azkaban managed to film almost all the Hogwarts interiors at the studio. Parts of Hogwarts that were previously portrayed by real-life locations either go unseen in this film or else are substantially altered. For instance, the area of Hogwarts that was previously represented by Alnwick Castle is replaced in this film by the Clock Tower Courtyard. However, there is still one real-life location that represents a Hogwarts interior in this movie. The staircase leading to Trelawney's classroom is actually the Geometric Staircase at St Paul's Cathedral. This is the first time that the Geometric Staircase is featured in the series, and it recurs in later films, with the in-universe location that it leads to changing twice.
Daniel Radcliffe named this as his favourite film in the series (Chamber of Secrets is his favorite book).
According to the published diary of Alan Rickman, he regards the film adaptation as the best and most daring of all the films in the series.
Creator-Preferred Adaptation: J. K. Rowling said this was her favourite of the films, saying she got goosebumps watching some parts of it. She also mourned the fact that she didn't think of the shrunken head herself while writing the book.
Deleted Role: Sir Cadogan, played by Paul Whitehouse, was cut almost completely out of the film. In the final cut, he only shows up in the background of the scene where the Fat Lady disappears.
Deleted Scene: Interestingly, the DVD came with a deleted scene showing the aftermath of Sirius Black's attack on Gryffindor Tower, an event from the book that doesn't occur in the film. However, the DVD didn't include a deleted scene showing the actual attack. The decision to delete the whole sequence was presumably made before the actual attack would have been filmed.
Executive Meddling: The GBA game was hit hard by this.Electronic Arts didn't trust the former GBC team at Griptonite Games to create quality GBA art, and ended up forcing them to completely change the art style halfway through development. With only half the time to complete the game, the developers had to cut many features and work crunch mode for the rest of development, including weekends and holidays.
Money, Dear Boy: Gary Oldman took the role of Sirius because he had not done a film in over a year (he'd just gained custody of his children from an acrimonious divorce and didn't want to travel constantly so he turned down roles to stay with them) and needed the work desperately. This turned out to be a positive version of the trope though as he gave a great performance, became good friends with Daniel Radcliffe while filming, and happily came back for the sequels. Combined with his role as Commissioner Gordon in The Dark Knight Trilogy, the role served as a Career Resurrection for him.
An inversion happened with Warwick Davis. As Flitwick wasn't in the script and Cuaron wanted to use Davis anyway, he had him play the conductor for the school choir. Later films retconned this to being Flitwick anyway.
This almost happened to Dudley, as Harry Melling had lost a lot of weight in between films. They ended up just putting him in a fat suit.
Playing with Character Type: Gary Oldman is well-known for playing villains, so when he was cast as Sirius Black, a mass-murderer after Harry, no one was surprised. By the end, it's revealed that Sirius never murdered or betrayed anyone, and in later movies he becomes the closest thing Harry has to family (naturally, this came as no surprise to viewers who'd already read the books).
Sort of. At the time of filming Dawn French (the Fat Lady) was married to Lenny Henry, voice of the shrunken head on the Knight Bus.
Daniel Radcliffe had a crush on a girl during filming, and personally requested that he had his sleeping bag placed near hers during the conversation between Dumbledore and Snape.
Emma Thompson took the role of Professor Trelawney to impress her daughter.
Whether intended or not, this family friendly Harry Potter film was the very next film Cuaron directed after the sexually explicit, adults-only Y tu mamá también.
Throw It In!: Draco Malfoy eating an apple during the Care of Magical Creatures lesson with Buckbeak. Tom Felton used to sneak food into his robes and eventually this led to the pockets on his robes being sewn shut. The apple was something he snuck in when they were filming, and they kept the scene in.
Troubled Production: Huge amounts of heavy rainfall nearly destroyed the sets. Helicopters had to bring bags of gravel in to prevent them from being washed away. There were numerous other weather-related difficulties from shooting on location in Scotland. Alfonso Cuaron ended up loving the resulting look of the film, however.
Buckbeak can be seen pooping in the Care of Magical Creatures class. This is not the first recorded instance of a CGI animal pooing, but it is the first time it happens in a feature film.
The only Potter film to not gross over $800 million worldwide.
The only book in the series where no character (permanently) dies, and also where Voldemort does not appear in any shape or form. Unless you count Harry hearing Voldemort's laughter in a memory.
in the data. You can cheat your way into it, but it's Unwinnable, as the "catch the mug" routine was either removed or never finished. It was cut at the last minute due to concerns about legal issues.