Revealing mistake: After the trained chimp is shot and is crawling into the cage, they show a shot of an ape turning around. You don't even have to look hard to see it but there's a two inch strip all the way down his face with no makeup. Clear as day. (01:41:30)
Revealing mistake: The humans on the planet live a prehistoric existence with little technology, however, they seem to be remarkably good at making foundation garments. Estella Warren spends most of the movie running around in nothing but an animal skin and yet her considerable assets are always held firmly in place.
Revealing mistake: When one of the people on Mark Wahlberg's team runs to a huge ape after an ape has escaped Paul Giamatti gets his hand cramped by the big ape. You can see a slight grin on his face, so you know he's not really hurt.
Answer: To prevent anyone else from learning that Leo came from space. After Pericles' ship crashed, there was a prophecy of a second coming of Semos, the founder of Ape civilization. Thade wants to kill all humans, so if anyone found out, it would be considered a sign and the council might consider making peace with the humans.
Captain Defenestrator