Trivia: When Hagrid is welcomed back to Hogwarts and everyone stands up and applauds, Vincent Crabbe also stands up and starts to applaud as well. This wasn't in the script and Tom Felton, staying in character, quickly grabbed Jamie and pulled him back down.
Trivia: In the scene where Harry and Malfoy are flying on their brooms, there's a shot where Colin takes a picture. Listen to the music right after that. The music is the same music used in Star Wars: Episode II - Attack of the Clones during the chase scene on Coruscant (John Williams did the music for this film and all the Star Wars films).
Trivia: When Harry, Ron and Fang begin to walk through the Dark Forest there is a close-up of Fang walking towards the camera. At the start of the next shot, at the bottom right of the screen the Ford Anglia is visible. Although the scene of them seeing the car before it rescues them is deleted, this one shot remains of the car 'watching' them. (01:43:40)
Trivia: The first scenes in the movie are some of the last scenes filmed. Viewers kind of tell by the way the actors' voices and looks changed. For example, Matthew Lewis (who played Neville Longbottom) said that he had to stuff cotton balls in his cheeks in the "Mandrakes in the Greenhouse" scene, since he had lost so much weight since the beginning of filming.
Trivia: There is an extra scene after the credits. You see the after effect of Lockhart's backfire of the 'Obliviate' spell.
Trivia: A trait of J.K. Rowling is to make up names that are pertinent or descriptive of their object/person (eg. Diagon Alley, Voldemort, etc). This is the same for Knockturn Alley: It is a place you wouldn't want to visit 'nocturnally'.
Trivia: Actor Hugh Grant was originally asked to play Gildroy Lockhart, but turned down the offer as he had already started working on another film.
Trivia: Jason Isaacs (who played Lucius Malfoy) liked the silver-tipped cane that he carries around so much that he tried to sneak it off the set, and was most displeased when he was caught.
Trivia: In Dumbledore's office at the end of the movie, the dialogue between Harry and Lucius Malfoy ("Let us hope that Mr. Potter will always be around to save the day"...) was improvised by Daniel Radcliffe and Jason Isaacs.
Trivia: Moaning Myrtle is played by Shirley Henderson who was also in the movie "Bridget Jones' Diary" (2001). Henderson's first appearance in that film is her standing in a bathroom crying, also what Moaning Myrtle does in her part of the film.
Trivia: The part of young Moaning Myrtle is played by Shirley Henderson, who is a 37 year old woman.
Trivia: In Philosopher's Stone (2001), Hagrid taps the bricks behind the Leaky Cauldron and as the bricks start to rearrange themselves creating the doorway, pause the film for the quick glance at the old green sign that reads, "Flourish & Blotts" which hangs over the corner bookstore. This is the bookstore in Chamber of Secrets that Harry and Hagrid pass on their way out of Knockturn Alley, but the old green sign obviously reads something else as it is not the setting for Flourish & Blotts in this film.
Trivia: As Harry enters Prof. Dumbledore's study, a portrait of Gandalf the Grey (from "The Lord of the Rings" books) is included in the collection of the great wizard paintings. It is above the door frame and slightly to Harry's right. (01:13:55)
Trivia: In Asian releases of the film, the Chinese subtitles for 'Draco Malfoy' has a double meaning. It is pronounced as 'zhuai ge', which also means 'arrogant guy'.
Trivia: Christian Coulson landed the role as Tom Riddle, even though he was 23 at the time of filming, and exceeded the 15-17 age group set for auditions. Ironically, in 2007 when Coulson expressed an interest in returning for Half-Blood Prince, director David Yates declined, feeling that Coulson was "too old" to play the role again.
Trivia: As Hagrid and Harry are walking away from Knockturn Alley, look closely in one of the shop windows in the background - there's the entire set of the Harry Potter books written at that point. (00:17:10)
Chosen answer: After Harry hands it to Lucius, Lucius hands it to Dobby to carry. After Dobby is freed by the hidden sock and protects Harry from Lucius, Lucius leaves it behind.
Greg Dwyer