Other mistake: When "the killer" is pumping gas, if you count the clicks associated with a liter going into the tank, they equal a total of 33 liters of gas, not 27 which is what the pump stops on.
Continuity mistake: When Marie is in the back of the van taking the chains of Alex, Alex picks up the knife and it is obviously bent. Once the chains are off and Alex puts the knife up to Marie to defend herself the blade is straight, and stays that way even when "the killer" takes it out of his chest.
Question: The killer arrives at the farm in an old rusty truck which Maria stows away in with the captive Alex. Then from the gas station she follows the truck in the murdered station attendant's car, and both vehicles end up at the scene of the final confrontation. Yet at the end we learn that Maria is actually the killer and has insanely hallucinated virtually the entire movie. Can anyone offer any explanation of where that big truck came from in the first place and what the truth is about which vehicles were really present at the end and how exactly Maria and Alex arrive at the scene of their final confrontation?