In the beginning scenes, where Milo Thatch is practicing 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.
During the sequence with the explorers' huge submarine submerging, one of the computerized "extras" can be seen waving at the camera. (He is seen through the lower window for only a second or two; use frame advance to view it or listen to the Visual Commentary on the DVD for specifics).