Revealing mistake: When Kurt is being chased after in the truck at the end, he pulls out onto the main highway and the truck skids. There are several tire marks where they practised this skid before. Also, at the very end when the truck is being pushed by the semi, look ahead of the front truck tire, more previous tire marks. (01:21:20)manthabeat
Revealing mistake: When Jeff and Amy are being chased by Red near the end and Red's truck begins to jackknife, you can see how they made the trailer slide in that direction. It seems that they constructed or used a trailer that had a set of wheels that would turn. They were turned in the direction of the slide.