Revealing mistake: While being hurled around by the Whomping Willow, Hermione grabs hold of Harry's shirt in the close-up. In the next shot as Harry's being lifted up, the bottom of the left side of his blue tee shirt is pinned to his pants, also visible in another shot. (01:29:30)
Continuity mistake: After the incident with the Whomping Willow, the dirt smudges all over Harry and Hermione's clothes change appearance and/or position in the following shots. (01:29:30)
Continuity mistake: At Shrieking Shack when Lupin says "You sold James and Lilly to Voldemort, didn't you?" to Pettigrew, you see Pettigrew holding onto the piano with his left hand. Next shot he isn't holding onto it. (01:32:00)
Continuity mistake: When Harry says, "I said we'll take you to the castle," to Pettigrew, you see Sirius pointing his wand at Pettigrew. When it cuts Sirius is standing next to Harry, but he is no longer pointing his wand. (01:32:45)
Revealing mistake: In the Shrieking Shack, when Harry sends Snape flying into the bed, the canopy collapses in the stunt. In this shot the metal bars at the top of the canopy frame are visible, whereas in the following shots it is no longer there. The way the canopy frame actually hangs after stunt differs considerably and the draperies hanging on the bed differ in the shots prior, during and after the stunt. (01:33:55)
Continuity mistake: Harry moves closer to Snape at the Shrieking Shack, as he points his wand at the professor. In the first two shots Snape stands closer to the door, yet in the close-up as the spell hits he is farther from the doorway, so he can easily fly backwards for the stunt. (01:34:00)
Revealing mistake: At the Shrieking Shack, when Harry shouts, "Expelliarmus!" there is a nice close-up of Snape and it is obviously not Alan Rickman flying backwards onto the bed. (01:34:00)
Revealing mistake: Just after Harry attacks Snape at the Shrieking Shack, he insists on knowing about Peter Pettigrew. In the next shot, as Lupin says, "He was at school with us. We thought he was our friend," there are wedges under the wheels of the piano, however, in the following shots they're gone. (01:34:10)
Continuity mistake: At the Shrieking Shack, when Scabbers tries to run away, as he runs towards the small hole in the wall, the shape of the hole differs in the shot facing the rat's hind and the next shot facing Scabbers, just as he enters the hole. (Obviously before the hole enlarges to accommodate Peter.) (01:35:05)
Continuity mistake: In the scene where Sirius lies at the lake and Harry kneels next to him, Sirius seems unconscious, then opens his eyes in terror as he sees the Dementors. However, in the very next shot, which shows the two from above, his eyes are suddenly closed and there's no sign of movement in his face. Too big a change, too fast. (01:38:45 - 01:42:50)
Continuity mistake: When Harry and Hermione are back in time, Lupin's transformation happens a lot faster than the first time. Also, the first time, Hermione shouts "Harry!", then Sirius yells "Run! Run!", then Lupin howls. The second time it goes "Harry!", then howling, then "Run! Run!" (01:39:45 - 01:57:40)
Continuity mistake: When Harry first sees the Patronus with Sirius, from Harry's POV it is clear that the Patronus light contracts entirely into the wand, while the area around the wand is still visible, and then he collapses. However, when Harry casts the spell later into the movie, Harry collapses on the other side of the lake, while the light from the wand is still quite large. (01:41:00 - 01:57:00)
Continuity mistake: When Harry collapses next to Sirius after the Dementors have been repelled, the ground where his head lands is covered in fairly small stones. In the following overhead shot of Harry and Sirius, there are some much larger rocks next to his head, and a patch of dirt with no stones is visible to Harry's left, where stones were before. (01:41:00)
Continuity mistake: Immediately after Remus' and Sirius' fight (as werewolf and animagus dog), a wounded Sirius stumbles down a pathway towards the lake. Harry is only a few steps behind him. When the scene cuts to the next shot, Harry is now running down a wooded slope alone and spots Sirius lying next to the lake. Sirius, in his weakened and injured condition, could not have sprinted so far and so quickly ahead of Harry. The terrain isn't steep enough for Sirius to have rolled all the way to the edge, and he wouldn't have had time to get up and continue walking. (01:41:50)
Revealing mistake: In the first overhead shot as the Dementors swoop down towards Sirius and Harry, Sirius lies in a particular position. During the Dementor attack his clothes move, then after Harry's Patronus repels the Dementors, Sirius breathes again and he now lies flat. After Harry collapses, in the last overhead shot, Sirius and his clothes lie in precisely the same position as the first overhead shot. His position differs later, in the repeat timeline as well. (01:42:50 - 01:45:20)
Continuity mistake: The chain on the Time-Turner changes length from when they go back in time, and to when Hermione explains the Time-Turner to Harry, one minute later. (01:43:15 - 01:44:35)
Other mistake: When Harry and Hermione travel back in time with the Time Turner, Hermione states that the time is 7:30, we then see them run to Hagrid's shack. As the camera passes through the clock on the castle, it shows the time is either 2:00 or 12:10. As well as this we are told that Buckbeak is to be executed at sundown, but he is executed in broad daylight, looking more like midday. (01:43:40)
Factual error: In the scene immediately following Harry and Hermione's travel back through time, she tells him, "It's 7:30." The clock, however, is striking the bells for an hour, not a half-hour. (01:43:45)
Revealing mistake: When Harry and Hermione have gone back in time and they are running across the courtyard beneath the clock tower, you can tell this shot is using CGI because they seem to be running faster and further than the number of steps they are taking. (01:44:05)
Continuity mistake: In the first scene when Harry and Sirius are by the lake, Harry sees someone conjure a Patronus on the other side; initially the silvery form of a stag is seen for quite awhile, then the circular light that broadens. However, after Harry and Hermione go back in time, as the shot faces Harry, he yells, "Expecto Patronum!" and immediately the wand emits circular light that magnifies and repels the Dementors. (01:44:05 - 02:01:00)
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 ★