Continuity mistake: In the Boggart scene, right after Professor Lupin tells Parvati to go and face the Boggart and it shows Harry high-fiving Ron, in the background you can see Seamus start to walk towards the front of the classroom, but he is standing behind Dean Thomas seconds later in the next shot. (00:41:40)
Continuity mistake: When Potter is looking at the 'Jack in the box' you can see Lupin in the background flipping his wand forward. When it cuts he has his hand and the wand behind his back. (00:42:10)
Continuity mistake: When Harry is facing the Boggart shaped as a clown, as Lupin says "Wonderful, wonderful" in the background, we can see Hermione standing right next to another girl behind Harry. But when it cuts to a wide shot from beside them we see Harry standing and we see Hermione standing behind him, but the girl next to her is nowhere in sight. (00:42:10)
Continuity mistake: In the Boggart scene, Lupin jumps in front of Harry to stop him from facing the Boggart. Between the shot directly before he jumps and the shot where he jumps, there is a dramatic change in his hairstyle. (00:42:20)
Continuity mistake: When they're having their first Defence Against the Dark Arts lesson and Harry is facing the boggart, Lupin jumps in front of Harry because he thought it would turn into Voldemort, as he later states in the movie. But the boggart had already turned into a Dementor before Lupin makes a move. (00:42:20)
Continuity mistake: After Neville's Snape/Gran Boggart, Lupin says, "Wonderful...to the back Neville. Everyone form a line." In the next two shots, first Neville heads to the back, then Malfoy shoves Neville to the side and Crabbe pushes the line of kids forward. Yet in the next shot from the front of the line, Neville already stands at the back of the line and then in the next shot, Neville walks towards the back of the line, where more kids are gathered now. (00:42:35)
Continuity mistake: When Parvati is stepping up to the Boggart, Harry is standing behind her, but while it's Parvati's turn it is not Daniel Radcliffe, it's noticeably his stand-in instead. (00:43:30)
Continuity mistake: When everyone, except Harry, leaves to Hogsmeade village, Hermione is waving as she and Ron walk directly behind McGonagall, with the last of the crowd of children ahead of them still in the courtyard. There is a short cut facing Harry now standing IN the doorway. Then the next shot from behind Harry, shows Ron and Hermione still walking past the fountain, but now McGonagall and the entire crowd of children are out of the courtyard. They could not have walked away that fast. (00:43:35)
Continuity mistake: During the DADA lesson, as Lupin jumps between Harry and the Boggart, to their right there are two tall containers, beside one another, standing against the wall with different items in them. The items change in the following shots, including the 'mirror reflection' shot. When the balloon whizzes past the back of the class and the camera spins around, the two vases are much farther apart, but in the next shot facing Harry, they're together again. (00:44:05)
Revealing mistake: During the DADA class, as the Boggart balloon flies by, Lupin's eye contact with the balloon, as well as others', are not quite in sync as they follow the balloon with their eyes. (00:44:15)
Revealing mistake: During the DADA lesson with the Boggart, the body double for David Thewlis (Lupin) is quite evident in some close range, head on and side shots. As a matter of fact, Emma Watson's and other actors' body doubles are very noticeable in many shots not involving a stunt. (00:44:15)
Continuity mistake: During class, as Lupin's Boggart turns into a wheezing balloon in the first shot it passes Harry and heads to the back, however, in the next shot the balloon is still in front of Lupin. (00:44:15)
Continuity mistake: When they discover The Fat Lady is gone from her painting as the Head Boy says "Let me through. Excuse me, I'm Head Boy." you can see Potter, Hermione, Ron and Neville change position between the shots. (00:45:55)
Continuity mistake: During the scene where the Fat Lady is missing, the students are gathered on the stairs and Fred and George are on the top of the stairs, right next to each other. In the shot right after Ginny says, "The Fat Lady, she's gone," one of the twins is on the left, at the foot of the other staircase. He could not have moved that fast, because the two are standing beside each other when Ginny talks. (00:46:05)
Other mistake: On the Dutch edition of the POA DVD, you can choose either English or Dutch audio. During Snape's werewolf lesson, he demands the students to "turn to page 394". On the Dutch audio version Snape demands "page 349" (considering the way in which the Dutch pronounce numbers an understandable mistake, but still a mistake), and it occurs each time Snape demands for this page. However, the Dutch subtitles oddly enough get the correct translation of the page number. (00:49:35)
Continuity mistake: At Snape's class when Hermione shows up and Ron says "Did you see her come in?", you see Potter turning around facing Hermione. When it cuts to Snape saying "Now, which one of you can tell me the difference..." you can see Potter is now looking at his book. When it cuts back Potter is facing in Hermione's direction again. (00:50:20)
Continuity mistake: When Snape is insulting Hermione on being a know-it-all while he is substituting for Lupin, he has a slide show running. The shot shows Hermione with the projector behind her. The projector now changes slides fully and stops moving. When the shot changed back to Snape, the slide is still changing. It could not be the next slide because the slide changes every few seconds. (00:53:00)
Continuity mistake: At the hospital, after Potter fell off his broom as Hermione says "No one blames you, Harry", you can see Ron standing behind her. At this time we can see the letter "H" on the cloth that is wrapped around the broom. Later, the letter "E" is visible instead. (00:54:45)
Audio problem: When Harry and Hermione have gone back in time and are watching the Dementors attack, Hermione says, "You're dying." When she continues, "Both of you", her mouth is moving before the words are heard. (00:56:05)
Revealing mistake: In the scene in which Harry, under the guise of the Invisibility Cloak, is dragged by the Weasley twins into the castle by his arms, it's obvious that the twins are miming a person in between them. There is one point when they round the corner right before throwing him onto the stairs, the twins are pretty much side by side, there is absolutely no room between them for a person at that point. They then widen the space again right after they round the corner. (00:56:55)
Chosen answer: It's not known what it is. It is left to the audience's imagination of what exactly is in the room or what some witch or wizard was doing in there. This is only meant to be a humorous bit and is unrelated to the plot. It didn't happen in the book.
raywest ★