Trivia: The reason Susan Bones is in so many scenes with the Gryffindors, although she was sorted into Hufflepuff, is because the actress is Eleanor Columbus, the daughter of director Chris Columbus. Two of his other children are also in the movie.
Trivia: There's been some discussion whether Lucius Malfoy starts saying "Avada-" or "Vera-" after Harry freed Dobby. It's not so easy to decide in the English version, although the DVD subtitles say "Vera-". In the German version, it's a lot easier, he says "Avada-" without any doubt. So it seems either the translators did not read the original script, or Malfoy does say "Avada-" in the English version (and they tried to cover it up for some reason by using a different subtitle). For those who have not read past book three, "Avada" is the first part of the spell "Avada Kedavra", a powerful killing spell that is highly illegal in the wizarding world. This is why this piece of trivia is important - many fans are perplexed as to why dear Lucius was performing such a spell directly outside Dumbledore's office. Jason Isaacs was not told what spell to use for the scene, so he improvised and started to say the first one that came to mind. He did, indeed, say 'Avada', the first word of the killing curse.
Trivia: All of the scenes that included Richard Harris were done first because of his failing health (he eventually died from Hodgkin's disease on October 25, 2002 after filming was completed). The scene where Dumbledore and Harry are in his office at the end of the movie was done first because he had the most dialogue here (notice how young Harry looks in this scene).
Trivia: Though very obvious to British users of this site, it is most likely not as well known in the US. Fawkes the phoenix is most likely named for Guy Fawkes (1570-1606), a Catholic conspirator who tried to kill King James I and blow up Parliament in 1605 (the Gunpowder Plot) to avenge persecution of Roman Catholics in England. His plan failed, and he was arrested, tried, and executed. November 5th is Guy Fawkes night/bonfire night, when the failure of his plan is celebrated with fireworks and bonfires - the fires often have a "guy" on top of them, a stuffed dummy.
Trivia: While in Flourish & Blotts, Mr. Weasley says to Mr. and Mrs. Granger, "I understand other Muggles are quite afraid of you." This makes little sense unless you know that both of the Grangers are dentists.
Trivia: In the book, there is a minor side plot where Percy was hiding the fact that he had a Ravenclaw girlfriend named Penelope Clearwater, who was also attacked at the same time Hermione was. She is largely out of the movie, but in one scene, Nearly Headless Nick says hello to Percy and 'Miss Clearwater' walking side by side.
Trivia: At the end of the movie in the credits it shows the cast in order of appearance. However, we see that Draco Malfoy comes before Hagrid, but in the movie we first see Hagrid in Knockturn Alley and then Draco in the book shop. This is because on the DVD there is a deleted scene where we see Draco enter the store Harry fell into. Still a mistake because the credits should have been altered in line with the editing, but there's the reason. (02:34:45)
Trivia: As Harry looks at the album at the start of the film, he turns the page of wax paper, between the pages of photos and the imprint on the wax paper is clearly visible. The imprint is that of many spider webs on the thin page of wax paper. It is best seen frame by frame. (00:01:00)
Trivia: The prop team built a model Basilisk for when Harry stabs it. However, the team had trouble figuring out how to make the internal frame of the Basilisk light enough to be used on set. They were going to use a long and laborious process which would be very expensive, but one of the crew suggested aluminum ladders, which were strong, but also very light. They then sculpted the Basilisk skin around the ladders.