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: The homeless man attacks Kathleen and she screams. But it isn't until 5 minutes later that Sanger comes to her rescue, when he only left moments ago.