Revealing mistake: In the scene when the crazy guy is hit in the back with the axe, when he falls, the axe sways side to side a little bit, then stops a couple inches of center from before.
Revealing mistake: Obvious dummies are in the car's back seats just before it slams into the wall. (01:12:35)
Revealing mistake: When Jason breaks his hand through the door it's really strange how his hand makes a perfect square on the broken door. Telling that the door was already broken and then repaired loosely for the stunt.