Revealing mistake: At the hut, when Hagrid bends Vernon's gun, if you look closely, you can see that there is a mark on the gun. When Hagrid bends the gun, the bend is exactly where the mark is. This is most visible on the DVD. (00:13:35)
Suggested correction: This is not a mark. It is either a scratch or a small piece of dirt on the shotgun. No mistake here.
Revealing mistake: After Hagrid gives Dudley a tail, watch him in the background while Dudley runs around. It's easy to see it's not Robbie Coltrane but a body double (Martin Bayfield), who is also in a few other shots at the hut. (00:17:45)
Revealing mistake: When Uncle Vernon picks up the letters for Harry and tears them up, you can see cuts in the envelopes, in order to make it easier for him to tear all of them at once. (00:09:40)
Revealing mistake: The wooden board is already broken before the mail comes flying through the mail slot. (00:12:00)
Revealing mistake: In the shot where Harry is running through the wall for platform 9 3/4, the camera pans down slightly and you can see a rather stiff and fake looking Hedwig wobbling in her cage. (00:33:30)
Revealing mistake: After Hagrid says, "Dry up, Dursley, you great prune," in the next shot just as Vernon fires the bent gun, before the hole actually appears, the light at the muzzle end illuminates the floor above and the outline of the pre-made hole is visible. (00:13:35)
Revealing mistake: During the chess game the Queen attacks the Knight's horse that Ron sits upon. In this close-up just before the spear actually hits the side of the horse, the large hole, used to aid the stunt, is visible in the belly of the horse between the stirrups towards the hind legs. This hole is not in previous shots. (Visible in fullscreen DVD.) (02:05:10)
Revealing mistake: When Ron is hit by the Queen during the chess game, the stunt double is visible on the horse just a few moments before he falls. (01:59:00)
Revealing mistake: When Harry, Ron and Hermione are making their way back to the Gryffindor common room, Ron says 'She knows more about you than you do', to which Harry replies 'Who doesn't?' The "solid brick" staircase moves so that they have no place to go but the third floor forbidden corridor. If you pay attention to the staircase it can be seen that there is a good gap between the staircase and the one it connects to when it moves and that when Harry, Ron and Hermione run off the staircase to the corridor the staircase made of "solid stone" does an awful lot of shaking. (00:58:40)
