Continuity mistake: When Trelawney asks Ron to look in Harry's cup and read the tea leaves, the Grim within the cup is visible. When Harry looks in the cup the Grim is different, for example, it has an open mouth in this shot. (00:30:20)
Continuity mistake: When Harry is talking to Sirius (the first time), Hermione yells to Harry to get his attention about Lupin. In the background, you can see Hermione sitting next to Ron right as she starts to say "Harry." In the next shot, she is standing up farther away from Ron (this is visible in the widescreen DVD only).
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: After Harry leaves the Dursleys, Sirius the dog shows up behind a park bench surrounded by dimly lit thick bushes. When the Knight Bus arrives, the bench is visible across the street and now it's brightly lit and the trash container beside the bench is clearly visible. Then, before Harry boards he has one more look at the bench and it is just as dark as the first shot. (00:08:00)
Continuity mistake: As Lupin packs in his office, the gramophone and books on his desk are visible in many shots. When Harry first walks in, the set of three thin books, bound with a string at the top of one pile, as well as the gramophone and other books noticeably change their position in quite a few shots. (02:06:10)
Continuity mistake: When Trelawney is looking in Neville's cup, a white cup is in front of a saucer on the table. When it cuts the cup has moved to the other side of the saucer. (00:28:55)
Continuity mistake: In the DADA class, when Lupin puts the needle on the horn gramophone disc to start the music, the position of his hand and the needle in the close-up differs greatly than in previous and following shots. Throughout the scene the gramophone and its horn's position differ in consecutive shots as well. (00:40:30)
Revealing mistake: After Ron has been dragged down the hole by the Grim, you see both Harry and Hermione get hit by The Whomping Willow and they fly backwards and land on the ground. Notice when Harry places his left arm in the ground, the ground is unnaturally soft. (01:25:00)
Other mistake: After receiving the new Firebolt Harry runs outside to use it. In the close-up as he takes off and in the next wide shot many of the students' eyes are not in sync with Harry's flight. (02:09:15)
Continuity mistake: When Marge floats off, Vernon is holding onto her, and Marge's dog is biting Vernon's trouser leg. In a closeup the dog is pulled well onto the Dursely's back lawn, as he bites Vernon's trouser leg, yet in a following wideshot the dog is dragged from the patio and onto the lawn once again, whilst biting the trouser leg. (00:05:25)
Other mistake: Right before Ron pushes Harry towards Buckbeak, you can see him glance to the right several times, as if waiting for a cue. (00:32:40)
Continuity mistake: When Harry lifts the lid in the Honeydukes cellar, in the first shot there are two gold pots, small and large, beside the table directly in front of him. Of course in the next shot, as the man climbs the stairs, only the short gold pot is beside that table. In the next shot, as Harry climbs out, the two pots' positions differ. (01:00:45)
Continuity mistake: When Harry goes to unchain Buckbeak, in the closeup he is holding the metal ring with his left hand after getting nipped by the crow, yet in the following wideshot his hand is below the ring, and he is now holding the metal chain. (01:48:40)
Continuity mistake: At the start of Hagrid's lesson, he coughs and says, "Ta-daa!!" for all to see Buckbeak. In the next wide shot Goyle stands at the back and his hood and robe lie flat. In the next close-up Goyle's hood is positioned completely differently, then in the next wide shot it's flat again. (00:33:20)
Continuity mistake: After Harry boards the Knight Bus, Stan hands him his ticket. In the shot facing Stan he folds the paper and holds it between his index and middle fingers. However, in the shot facing Harry, the paper is straight and he holds it between his thumb and index finger. (00:09:30)
Continuity mistake: When Harry and Hermione travel back in time, Harry walks towards Buckbeak, planning to save him. There are pumpkins around Buckbeak and there is also a black cauldron near him too. The pumpkins and the cauldron move between shots during the scene as do other items in the background, and nobody touches them. (01:48:25 - 01:49:25)
Continuity mistake: Before Hagrid's lesson begins, Malfoy yells, "Dementor! Dementor!" and they all spin around. Ron and Hermione stand beside one another in the first and third shots, yet in the middle shot facing Malfoy, they're a good distance apart. As a matter of fact, in most shots throughout this entire scene many of the students' positions and actions change and/or shift back and forth in consecutive shots, some quite drastically. (00:33:00)
Continuity mistake: When Dumbledore first introduces Lupin as the new Defence Against the Dark Arts teacher, the camera pans to the Gryffindor table. You can see that Ron and Hermione are sitting opposite each other with their dinner sets in front of them. Then Malfoy insults Harry, then when it cuts to Ron saying "Shove off Malfoy" Ron is now sitting opposite the girl who was beside Hermione and not Hermione herself, and the girl couldn't have just moved across because all of her dinner set is in front of her too, perfectly set out. (00:24:05)
Continuity mistake: At Hagrid's, when Harry, Ron and Hermione visit the first time, the quilt lying on the chair changes position over and over again, from lying over the back of the chair, to being on the seat and so forth, until Hagrid takes it to cover his little creature. (01:24:35)
Continuity mistake: In the shrieking shack, the cobweb on the ceiling changes position between shots.
Chosen answer: Fred and George used the map to aid them in their mischievous activities at Hogwarts, and probably had little interest in what their little brother was doing or who he might be with at any given time.
raywest ★