Revealing mistake: When Caleb shows Mae his horse and it rears you can see the man holding the horse's rope is not Caleb. The man has an older, redder face and greyed sideburns. (00:08:21)
Revealing mistake: The principal apprehends the two younger and bigger guys at once (and for some reason they don't gang up on him and kick his butt). The other guys in the Chevy decide to get back in and drive away. You can already see on the dirt the path they will follow, which is logical for the bit in reverse but not so much for the part when they turn left and go forward, which is not how the car could arrive to that point. And when later the car circles around, it moves also on a path that was not showing in the first shot. (00:11:50)
Revealing mistake: When Harry screams through the windshield of a car you can see the actor's mouth and teeth inside of Harry's mouth.