Deliberate mistake: When the lady is supposedly in the water with the crocodile, you can see that it isn't her. It is actually Steve in a fat suit and wig.
Visible crew/equipment: When the lady hunting the crocodile falls out of the tree and is supposedly holding herself up by one hand, you can see the harness under her shirt, and the strap that's really holding her up.
Visible crew/equipment: When the CIA Agent is being dragged by Steve and Terry's truck during one shot you can see the edge of the hidden board upon which the stunt man is actually riding on.
Revealing mistake: When Steve and Terry first attempt to catch the rogue crocodile in the river, during several shots you can see that the river bank is concrete and fake rocks.