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.)
Continuity mistake: When the students are dancing to The Weird Sisters at the Yule Ball, Viktor Krum can be seen at the back of the group, jumping up and down, with Crabbe/Goyle jumping up and down behind him with his hands on Krum's shoulders. Immediately after, however, Krum is seen dancing with Hermione, and Crabbe/Goyle has disappeared, with no time to move between shots.
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: During the Tournament's first task, Harry runs behind the large rock formation to hide from the Horntail. After he's summoned the Firebolt, as he's crouched down, there is a semi close-up of Harry, then it cuts to a close-up, and the position of his red and black hood on his shoulders noticeably changes between these shots.
Other mistake: When Barty Crouch Jr., as Moody, near the end of the film says about him providing Neville Longbottom with the book for the Gillyweed, Harry is mouthing his lines (before his close-up).
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).
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: 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.
Continuity mistake: After Harry overhears the conversation between Snape and Karkaroff, Snape holds up the small glass bottle of Veritaserum while he accuses Harry of stealing from his store of ingredients. The way Snape holds the bottle repeatedly differs between the close-ups facing Harry and close-ups facing Snape.
Continuity mistake: There is a scene where Harry is holding the letter from Sirius and we can hear Sirius's voice reading the letter. The words on the letter are different from the words we hear Sirius reading. Particularly the end where Sirius says, "P.S. The bird bites" the letter says, "By the way, the bird bites."