Deliberate mistake: When the Norwegian starts shooting at the dog, Childs jumps into the snow and you can see the shape before he jumps in where he's had to do this before on different takes. (00:08:40)
Deliberate mistake: After Chris gets stuck on the bridge and is trying to restart the van, a shot out the back window shows Jason running towards the van. He is badly limping and holding his knee because Chris just stabbed him in the knee. In the next scene, when Jason is chasing Chris away from the van, and for the remainder of the movie, Jason no longer limps. He walks and runs normally.