Deliberate mistake: When bars are placed on Harry's windows, so he does not escape, it is apparent that his windows have complete leaded panes of glass. Yet when Harry is being rescued, Ron and Harry speak with each other, even in low voices, through his visibly closed windows. (00:08:00 - 00:09:00)
Harry Potter and the Chamber of Secrets (2002)
1 deliberate mistake - chronological order
Directed by: Chris Columbus
Starring: Maggie Smith, Alan Rickman, Kenneth Branagh, Richard Harris, Daniel Radcliffe, Jason Isaacs, Emma Watson, Robbie Coltrane, Tom Felton, Rupert Grint, Richard Griffiths
Genres: Adventure, Family, Fantasy, Harry Potter, Mystery
Revealing mistake: At the beginning of the scene near the end of the movie with Lucius Malfoy fuming at Dumbledore in his office, Malfoy's hair is fanned back behind his shoulders. The lighting in the room illuminates the back of his neck, where you can see his real, short brown hair. (02:22:05)
Uncle Vernon: And Dudley, you will be?
Dudley Dursley: I'll be waiting to open the door.
Uncle Vernon: Excellent. And you?
Harry: I'll be in my bedroom, making no noise and pretending that I don't exist.
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).
Question: Is this true that line "I didn't know you could read" was improvised by Tom Felton, who forgot his original line?
Answer: Yes in the same way Daniel Radcliffe improvised his line about always being around when talking to Lucius at the end.
Actually, Jason Isaacs said that, and he and Daniel didn't forget their lines but did it intentionally.
Answer: Yes. It's a common occurrence in a lot of movies for actors to forget their original lines so they improvise something to help move the scene along and not break character. Tom did this because he forgot what his original line was.