In season 4 episode 19 "Jumping the Shark" one of the ways they test Adam is with silver but he doesn't react to it and Sam mentions later that as a ghoul he wouldn't but in this episode Sam says that the monster's reaction means he could be a ghoul.
When the shape shifter posing as Dean shoves real-Dean, it looks like he pushed at his shoulder in the first shot, but in the next shot his hand is at real-Deans throat.
The pillow and comforter on Dean's bed are bunched after he uses the Magic Fingers, but they are seen undisturbed as he is thrown to the wall during his fight moments later.
When Sam is speaking with the father there is a blue Chevy Nova SS right outside the door. When the camera pans out its gone.
When Dean is having Lisa show him that she knows how to load the gun and use it, she calls the magazine a clip. Inaccurate.
When the shapeshifter posing as Samuel is shot by the Campbells with tranquilizers, his back is to the camera and he is obviously wearing some sort of thick vest underneath his shirt that the darts are embedded in. This vest can also be seen when he turns in profile and somehow ejects the darts out of his back.