Revealing mistake: During the monsoon scene, everyone is on a table trying to climb on the chandelier. Peter has been turned into a monkey, and his face is covered in hair and has the characterists of a monkeys face, yet in shots when they are on the table, like when the crocodile snaps at them on the table, just before Alan lifts Peter onto the chandelier, you can see the plain face of his stunt double, with no monkey features! Robin William's and Bonnie Hunt's doubles are rather obvious in these same shots too.
Revealing mistake: During the monsoon scene, Sarah has both her feet aginst the jaws of the crocodile, and so Alan jumps from the chandelier, and dives into the water. As he dives into the water, watch Sarah's feet, and her left foot slips into the crocodiles mouth, and his upper jaw slams down on it! The crocodile has a row of sharp teeth on at the front of it's mouth, which come down onto her shoe. That would be painful, yet she doesn't scream/limp/complain.