Continuity mistake: In the Great Hall, after Hermione quips, "Well spotted!" Ron imitates his brother (when he asked Angelina to the Yule Ball) by lifting up his arms to mimic dancing, and Snape promptly smacks the back of Ron's head. In the next shot, Ron holds a pencil in his formerly empty right hand. (01:11:15)
Continuity mistake: After Fred and George drink the aging potion, when the twins jump over Dumbledore's Age Line, in this overhead shot Hermione sits at the edge of the long bench, with the closed book and crossed legs. Yet, in the next shot, as Fred and George begin congratulating each other, Hermione sits a few feet away from the edge, still with the closed book and crossed legs. (This is before she moves her seat and opens her book.) (00:29:00)
Continuity mistake: In the DADA class, whenever there is a shot facing the class room, we can see that Ron and Harry are in the middle of the class room and Parvati and Padma are on the viewer's right side of the room (screen). Yet, when Moody makes the spider float from Padma onto Ron's face, in the shot facing Ron, the spider floats onto his face from the viewer's left side of the room (screen) whereas it should have been the right side of the room (screen).
Continuity mistake: At the Quidditch World Cup, when the kids reach the top, in the first shot facing them their positions are Cedric, Ron, Fred/George and Ginny. Just before the shot cuts, Ginny is just about to move behind a twin, and more to the point, three members of the Irish zoom by on their brooms between Ron and Cedric. In the next shot (from behind), as the Irish are still zooming by, now their positions are Fred/George, Ron and Ginny, with the Irish zooming by between Ron and Ginny. Between shots, Ginny has moved past three people and the zooming Irish on their brooms. Don't confuse the hat wearing twin for Ginny; her hat is green with a black buckle band and the twin's hat is green stripe. (Clearer on fullscreen DVD.)
Continuity mistake: When Harry's name has just come out of the Goblet, we see a shot of Hermione with Ron in the background. In this shot, Ron is looking up at Hermione. A second later from a different angle, Ron is looking down, then moves his head to glare in Harry's direction. Nobody can move that fast. (00:32:45)
Revealing mistake: At the first challenge, just before the Horntail makes its appearance, there is a tight close-up of the egg as Harry stands in the stone "doorway" in the background, on the left. Clearly it is not Daniel Radcliffe, but his stand-in (his face differs and he has a shorter, bowl-type haircut) who is standing there, for this one specific shot.
Continuity mistake: When Harry is on the Hogwarts Express, it is apparent that his scar is missing or very much out of place. Then during the second task, when Harry is swimming, the same thing happens.
Continuity mistake: During breakfast in the Great Hall, after Harry dribbles on himself, he and Ron are seated right beside one another and likewise their plates. When Nigel brings the box, all of a sudden there is a huge gap between them and a convenient open space on the table to place the box. (01:05:05)
Continuity mistake: Right before the third task, Igor Karkaroff puts his hands on Krum's shoulders. In the next shot, however, his hands are off his shoulders and he is standing a respectable distance away. This change continues throughout the rest of the scene.