Continuity mistake: When the car is crashing, in the long shot it looks like Rob's arm is hanging out of the car window. But when the shot is from the inside of the car, Rob doesn't have his arm hanging out.
Continuity mistake: Near the end of the movie, Marvin meets up with the doctor who tells him that something else is in the woods doing the killing. They both take off running and the doctor falls flat on his back. Marvin turns to go back to the doctor, and the doctor is now sitting straight up and not in the same spot he fell at.
Continuity mistake: When Rob is falling off the cliff in his car, the dents on the car appear, then appear somewhere else, then disappear completely, then appear again.