Other mistake: When Sam is selling his onions, he asks an old man to take his hat off so he can see if he's bald so he'll know if he needs to sell him some hair growing tonic. The old man is just barely taking off his hat and before Sam can even tell the old man has no hair, Sam says "Mm hm, just as I thought."
Other mistake: When Jason is in the corn field during the rave, after Jason breaks the guys neck, the other guy burns him with a torch and the flames burns around his neck area, which should have caused him to not have any hair. But throughout the movie, his hair is still there.
Other mistake: When Will's mother steps into the bathtub where his father is already lying in, the camera switches between both persons and the water level (in relation to the bathtub edge) on each person's side is on a different height. Yet when both persons are shown, we can see that the bathtub edge is fully horizontal, so the water level should be the same on both sides. (01:25:00)
Other mistake: After Gollum attacks Frodo and Sam on Mount Doom, Sam fights Gollum off with his sword. He then turns around and calls out for Frodo. There is a brief medium shot of Frodo scrambling up the mountain (at about 01:20:35 on disk 2 of special edition). If you look carefully in the background, you can see snow and running water in the background. This is common on Mt. Ruapehu, where the scene was shot, but a bit out of place on Mt. Doom. (01:20:35)
Other mistake: When first showing the Hoenn Pokémon League, the match is about to begin, but the screens for it are off. (00:00:56)