Continuity mistake: When Hagrid cries out, "Buckbeak's been sentenced to death!" in the close-up, Harry Ron and Hermione are visible at the shoreline behind him. However, in the next overhead shot Ron and Hermione are much closer to Harry along the shore. (01:12:50)
Continuity mistake: When Vernon says, "You've nowhere to go," to Potter, you see Vernon grab the banister. When it cuts, the way he holds the banister changes. (00:06:30)
Continuity mistake: When Trelawny says "Look at the cup, tell me what you see" to Ron, the way Ron holds the cup changes between shots. (00:29:10)
Continuity mistake: The second time Harry conjures the patronus charm to save Sirius and the other Harry from the dementors, Hermione is standing next to the tree behind him. The first time he uses it, his silhouette can be seen from the other Harry's point-of-view from across the lake, but Hermione isn't next to the same tree, even though the spot she was standing in is visible. (01:44:20 - 02:01:05)
Continuity mistake: When the stone hits Harry, the very first time, in the shot inside Hagrid's, he yells, "Ow!" and as he turns the blue cup touches the wood tray. In the next exterior shot, the blue cup is closer to the birdcage. (01:24:55)
Continuity mistake: The Monster Book of Monsters' torn papers change amount/position in subsequent side and top shots when there has been no movement on the floor by the book or Harry nor any floor shaking by the train either. (00:15:20)
Visible crew/equipment: In many shots throughout the film, there are noticeable reflections of either the reflector screen or studio/set lights, in the lenses of Harry's glasses, as well as Professor Trelawny's. (01:24:00)
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)
Visible crew/equipment: At the end of the film, when Harry enters Lupin's office, he walks past a cabinet full of skulls, saying "You've been sacked?" Reflected in the glass panel of the cabinet is a cameraman with equipment, moving along with the camera, a little above Harry. He's a little hard to see, but he's there! (02:01:30)
Continuity mistake: The cart with the TV changes its position in various shots. For example, in the close-up of Marge's legs lifting off the ground and when Marge floats out the door in the exterior shot, the cart is aligned with the doorway, then at other times it is at the inner edge of the draperies or in between. (00:04:10)
Continuity mistake: At the Leaky Cauldron, after Harry takes off his sneaker, to distract the Monster Book of Monsters, he stands at the edge of the bed. In the wide shot, the very long ends of the shoelace dangle over his fingers at his knuckles, yet, in the next close-up, it's now the short ends that are held tightly in his fist, the opposite way. (00:15:55)
Audio problem: As Sirius, the dog, drags Ron towards the Whomping Willow, Hermione and Harry chase after them. When Sirius actually backs up into the hole below the tree trunk, Ron begins to shout, "Help!" In the next shot, as Harry starts to stretch his arms forward to dive down, Hermione runs behind him and visually she shouts Ron's name, though there is no sound heard. (01:28:15)
Revealing mistake: Watch as Hedwig lands on Harry's arm. It's quite obvious he has some protection under the shirt sleeve as his arm and wrist is unnaturally thick. (00:14:00)
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: 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: At Hagrid's, after the jar breaks the first time, in the wide shot the toad is on the table, under the cracked pieces of jar, yet in the next close-up, the cracked pieces are gone and the toad is back on the blue plate. Later, when Hermione throws the stone, the toad is on the plate (which is farther from the jar now) as the jar breaks. (01:24:50 - 01:51:20)
Continuity mistake: In the boggart scene after Neville Longbottom has confronted the boggart, we can see that Ron is next, then Seamus Finnigan, then Parvati Patil. But after Ron's turn with the boggart, Prof. Lupin immediately calls out Parvati. Seamus never got a chance with the boggart even though he was right behind Ron. (00:41:10)
Continuity mistake: When we get to Trelawney's class when she says "...discover if you possess the sight.", she gets up from her chair. While doing so she place both her arms on the arm rest, but when it cuts her left arm is up. (00:28:10)
Continuity mistake: When Marge is floating off into the air, in one shot we see Dudley leaning back in horror and suprise, and he brings his arms back, off of the table and to his side. Yet in the following shot his arms are back to laying on the table and he lifts them up off the table again, but doesn't bring them to his side (he just lifts them up into the air). Then in the next wide shot they are laying on the table again. (00:04:45)
Continuity mistake: When Harry enters the room in the Leaky Cauldron that the Minister of Magic is in, Hedwig has arrived before him. The owl shown at the start of the scene is a white owl with many black spots on both its wings. However, when Harry leaves and Hedwig flies to his arm, this owl has very few spots at the edge of its wings and tail, obviously it's one of the other owls that portray Hedwig. (00:12:55 - 00:14:35)
Answer: This didn't happen in the book. It appears to be done purely for comic effect in the movie, showing Dumbledore's eccentric and quirky nature. He's seemingly oblivious to what he's doing and how it affects Ron.
raywest ★