Continuity mistake: When Dudley is lying on the ground, with the Dementor hovering over him doing his thing, notice the wall behind Dudley with huge white graffiti. First he is lying past that specific graffiti, closer to the entrance/exit, then he is lying 4-5 ft away, on the other side of that graffiti.
Continuity mistake: When Harry wakes up after dreaming about Mr. Weasley's attack, you can see stubble on his neck. However, when he is in Dumbledore's office and later in Snape's, his face is clean shaven. (01:05:30)
Continuity mistake: When Harry is standing over Bellatrix Lestrange near the end, pointing his wand at her, his fringe (bangs) changes position a few times between shots. (01:52:50)
Continuity mistake: After Sirius falls through the veiled archway, when Lupin grabs Harry he first holds him over his right arm, then under and once again over, between shots. (01:52:20)
Continuity mistake: During the interruption of the OWL examination, when Umbridge stands at the doorway to the Great Hall, she casts a very long noticeable shadow directly in front of herself, as she looks to her left. Next shot, as the twins fly past, she now casts a shadow perpendicular to the previous one, with the former one gone. (01:32:00)
Continuity mistake: In the Room of Requirement, before the Christmas holiday, Harry compliments the DA on a job well done, and they clap. There are two consecutive shots of the group from different angles, and between shots Cho's wand turns upside down and another girl's wand changes hands, etc. (01:01:25)
Continuity mistake: When the Dursleys leave in their car, there is a large hanging plant to the right of the front door with mostly large white flowers and some red. When Harry, Moody, Tonks and the rest leave the house, the flowers are now small and red. (00:06:50 - 00:08:40)
Continuity mistake: At the train station, when Moody sees Padfoot, Molly Weasley walks a certain distance behind Harry and the dog. Next close-up she is directly behind Harry, but when it cuts to the wide shot, she's much farther back again. (00:24:35)
Continuity mistake: In the opening aerial shot of the playground, the landscape surrounding it is flat, devoid of any shrubbery, and there are no buildings or streets nearby. In the close-up shots with Harry and Dudley that are shown from various angles, there are now houses, small hilly mounds, bushes, and a road in the background. (00:00:50)
Continuity mistake: While still at the Dursley's, Harry has a dream and wakes up. When he wakes up there is moonlight shining on his pillow, right near his face. When the camera angle changes, the moonlight on the bed where his face is is gone. (00:07:50)
Continuity mistake: Dumbledore wears a thin silver strand, with dangling silver balls, tied round his beard, and the position of this strand and height of the silver balls differ in consecutive shots, depending on the camera angle, throughout the film. For example, when Dumbledore stands before the Wizengamut during Harry's hearing. (00:20:30)
Continuity mistake: In the Gryffindor Common Room, when Hermione and Ron sit down beside Harry in the first shot, Hermione's left shirt ribbon hangs over her shoulder under her hair. When it cuts to the front shot, as she sees Harry's hand, that ribbon hangs properly down the front of her shirt. (00:39:10)
Continuity mistake: When Harry is sitting at the table talking and holding the Daily Prophet in his hands, he continually changes from holding the newspaper down on the table, to up in the air, and keeps on changing which side he is holding up as well. (00:15:10)
Continuity mistake: As Lupin restrains Harry from following Sirius into the Death Arch, the wand in Lupin's right hand alternates from pointing down to pointing up, then down again.
Continuity mistake: In the Forbidden Forest, Hermione dings the bell on the handlebar in the close-up as Grawp stands quite a few feet away with empty hands. Harry's and Hermione's eyes remain fixed on Grawp as Hermione dings the bell, so we know he does not pick up another handlebar. In the next shot, Grawp, still standing in the same place, dings the bell on the same handlebar; it changed hands between shots.
Continuity mistake: After riding down the escalator on their way to Harry's hearing, when Arthur Weasley tries to pass the turnstile, Harry's right hand reaches for the transit pass in his left jacket pocket in the side shot. Then he reaches once again in the front shot, before it cuts back to the side shot as he's still reaching for it. Also, note the man with the newspaper under his arm that passes the turnstile only to be back in line, between these shots. (00:17:10)
Continuity mistake: In scenes, but most noticeably in the court room scene, the tassle which hangs on Professor Dumbledore's hat keeps on changing position from whereabouts, and how it is hanging down. (00:22:20)
Continuity mistake: When Harry is being tested by Snape on being able to block his mind from being read, the sweat stain on his jumper (sweater) changes from larger to smaller during the scene. (01:07:00)
Continuity mistake: After Harry enters the Gryffindor Common Room, when Seamus stands up his white shirt is untucked just a bit at his back. As he stands with his hands at his sides, in the next shot from behind Seamus, now the entire shirttail is untucked. (00:32:10)
Continuity mistake: When the Dementor grabs Harry at the start, Harry's feet are apart. Camera does a quick cut and now one foot is tucked behind the other. (00:03:15)
Answer: Draco is shocked because a teacher is never allowed to hit a student, not for any reason. He never expected Umbridge to behave in such a manner.
raywest ★