Revealing mistake: When the mayor has his head shaved by the Grinch, Clint Howard grabs the clippers and shaves his own head down the middle. His hair is yanked off his head before he even moves his hand. Even better in slow motion.
Revealing mistake: When the Pterodactyl is flying around with the egg, its shadow isn't cast as she flies over the trees.
Revealing mistake: In the scene where Rudolph is saving Tony from the truck he says, "close your eyes, Tony". But in the next scene when they are on the blimp the boys introduce themselves. Rudolph did not yet know Tony's name but yet he said it.
Revealing mistake: In the scene where Rocky and Bullwinkle are walking through the university with Kenan and Kel (right before they come across the anti-moose protest), Kel's right arm passes through Rocky's left several times.
Revealing mistake: When Spencer is walking over to the computer, he clips through the rocking horse. (00:01:39)