Continuity mistake: As Buddy walks out into the street at the start of the movie when the cat is playing dead, you can see several parked cars on the street behind him. When the van backs up to 'catnap' buddy, there are no parked cars. Then as the van drives off again, there is a different bunch of parked cars in the street. (00:03:54)
Continuity mistake: As Boromir and Aragorn talk right before Boromir dies, you can see Boromir's right hand gripping Aragorn's left shoulder in the shot from behind Aragorn's right shoulder, but when the camera view changes to Boromir's perspective, looking up at Aragorn, his hand is not there. The scene goes back and forth between these two views several times. (01:22:40)
Continuity mistake: When the troll enters the girls' lavatory, in the wide shot as Hermione walks backwards towards the cubicles, the room becomes brighter from the storm. With this extra bright light it is simple to see that the wall between the 2nd & 3rd cubicles actually touches the floor, unlike the other cubicle walls. Yet, in the overhead shot as the troll's club slams into the cubicles, Hermione is lying under that very wall crawling away. (01:10:05)Super Grover
Continuity mistake: In the beginning scenes, where Milo Thatch is practising his proposal, he slides over (face forward, chest against the board) a chalk drawing of a map detailing the location of Atlantis. When he realises he wiped off the drawing, and sees it on his clothes, he stands in front of the blank part of the chalkboard, "filling in" the space with the map that rubbed off on his shirt - the only problem is, that the image should have rubbed off backwards as he was facing the board when it transferred to his clothes. He could not simply stand in the place of the missing map face forward and have it read properly.
Continuity mistake: In the scene just before the final attack on the castle, D'Artangan is surrounded by his fellow Musketeers. He gets off his horse and while doing so there is a tight close up where you see clearly that he is wearing his Musketeer outfit that he threw down on the floor in the previous scene. When he finishes talking to the horse (and he is back in his normal clothes) Porthos hands him the Musketeer uniform, which D'Artangan then puts on. (01:20:45)