Continuity mistake: In the paddock scene, Harry's tie changes length. When he is in the paddock the narrow end of the tie is longer. When flying on Buckbeak, his tie is properly even. Then when he returns to the paddock, his tie is uneven once again. (00:34:15 - 00:36:50)
Continuity mistake: When Marge floats out the patio doors after Vernon yells, "Stop!" there is a horizontal tear along the vertical one at the back of her jacket, that is gone in the last shot of her after Vernon lets go. (00:05:25)
Continuity mistake: When Snape points his wand at the Marauder Map and says, "Reveal your secrets," you can see Potter has his right hand down. When the scene cuts, his right hand is holding the map. (01:13:00)
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: When Neville opens his 'Monster Book of Monsters' he falls to the ground. Then he is lying on the ground and his book is attacking him again. We can see the pieces of pre-cut papers, that should be coming out of the book's mouth, actually come up from the ground, when Neville is holding the book above him. Obviously it's not real. (00:31:15)
Continuity mistake: When the Weasley's have given Harry the Marauders Map, after one of them says "We owe it so much", Harry opens the map. When it cuts he opens it again. (00:57:35)
Continuity mistake: When Hermione and Harry go back, when they are at Hagrid's things lying in his front yard, such as the cauldron, wood, etc., change position in the following shots. (01:52:50)
Continuity mistake: When in the Leaky Cauldron, there is a man offering Harry food. He holds a bowl of nuts towards Harry, and in one shot he holds the bowl with two hands, yet in the following shot he is holding it with one hand. (00:12:50)
Continuity mistake: The first time Harry, Ron, and Hermione leave Hagrid's hut before Buckbeak gets "executed," Hermione opens Hagrid's back door and all three are peeking out of it before Hagrid opens his front door. The second time, when Harry and Hermione are watching from the pumpkin patch, Hagrid opens the front door at about the same time that Hermione opens the back one, and Ron and Harry aren't even seen yet. Because this is the same event in time from two different points of view, it should be absolutely synchronized.
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 Harry storms into the pub in Hogsmeade, the camera follows his footprints to the door, and at the door is a large clearing where there is no snow, because the ground is sheltered by the door's porch. Yet in the following shot the clearing has decreased greatly. (01:01:35)
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: In the corridor when Harry shows the blank map to Snapes he is holding it only in his left hand. When the view switches he has both hands on it, and in the next shot is again holding it in one hand. (01:13:00)
Revealing mistake: When the students are running towards the portrait of the hippos where the Fat Lady is hiding, watch the railing of the stairs. It shakes back and forth, showing it isn't really made of stone.
Continuity mistake: Just before the Knight Bus starts to squeeze between the two double decker's, watch the annoying Shrunken Head at the front of the bus. There's a long shot as the bus is just about to squeeze, and the head turns round to face Harry. There's a shot of Ernie pulling the leaver, then a close up of the head as it turns round again, and says, "Mind your head." (00:11:40)
Continuity mistake: Outside Hagrid's, when Fudge says "We must search the grounds," the way Dumbledore holds his staff changes between shots. (01:50:15)
Continuity mistake: When Marge and the family are eating, Mr. Dursley pours Marge some brandy. She then tells him to pour a bit more, and in one shot he is holding the brandy bottle and glass away from each other, yet in the following shot he's pouring brandy into the glass. (00:02:35)
Continuity mistake: After Harry arrives at the Leaky Cauldron, Tom brings him to meet with Fudge. When Tom leads Harry to the chair in the wide shot, it is at a diagonal, but in the next close-up it faces the table head on. It changes in following shots as well. (This has nothing to do with the shape of the chair's arms.) (00:13:10)
Continuity mistake: When Snape and Harry are in the hallway and Lupin shows up and Snape goes, "Well, well, Lupin," you see Harry in the background attempting to tuck away the Marauder's Map in his pocket. When Snape grabs for it, he reaches up more, as if Harry is holding it more by his shoulder.
Continuity mistake: When Harry climbs out of tunnel into Honeydukes, the boxes on the stairs are straight up against the wall, including the box with the lollypops on the fifth stair. However, in the next shot from above, the box is farther from the wall for the effect. (01:01:00)
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 ★