Continuity mistake: In the scene where Dean uses the silver knife to cut his arm to prove he is not a shape shifter, a few moments later Dean is showing Bobby the hand print on his arm, and the cut is miraculously gone.
Continuity mistake: In this episode, Dean says he was born in 1979. In the first two seasons, in the flashback to their mother dying, that's in 1983 which would make Dean 4 years old. He's definitely not 4 years old in the flashbacks.
At the beginning, the cabin looks very similar to the cabin in The Evil Dead, even the swinging bench (although on the opposite side of the door). And the girl calls out the name Ashleu, Bruce Campbell's character in Evil Dead.