Revealing mistake: As Harry and Buckbeak fly over the loch, Buckbeak's foot trailing in the water leaves a wake, as it should. This wake should also disturb the ripples and waves that are already present on the surface of the water, but they do not. It is obvious that the wake effect was added in, but the foundation shot of the loch was not edited to help it make sense. (00:35:20)
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)
Revealing mistake: In the scene at night, when Harry is in the hallway with the map, the tip of his wand lights up. And later in that same scene, when Snape has the conversation with Lupin and Harry, Snape's wand does the same. However, if you look closely at the shadows on their faces, they're being lit from above, not from the wands' light below them. (01:13:45)
Revealing mistake: At Hagrid's lesson, just after Malfoy wound Harry up, there is a close up on the class when they first see Buckbeak and you can see Emma Watson holding back a laugh. Surely if her friend was being picked on it wouldn't be funny, plus they're supposed to be scared of Buckbeak. (00:32:05)
Suggested correction: Not true. I saw this scene several times and I never saw Hermione holding back a laugh.
Revealing mistake: In the punch scene "replay", Harry is noticeably stockier, and I would suggest shorter, and he walks in a very unusual way - very different from Harry. Obviously a double.
Revealing mistake: When Mr Weasley is warning Harry about Black wanting to kill him there is a jug in the background supposedly magical because it is serving the drinks by itself. If you look closely you can see the wire or string or whatever held it up.
Revealing mistake: At the Shrieking Shack, when Harry shouts, "Expelliarmus!" there is a nice close-up of Snape and it is obviously not Alan Rickman flying backwards onto the bed. (01:34:00)
Revealing mistake: When Hagrid stands up and nearly knocks over the table, McGonagall's goblet manages to stay rooted to the spot.