Puppet Master - Bloody Face
It's toward the end when Alex is being punched by the "Puppet Master" and his mouth is all bloody. The camera then shows a shot on the girl (I can't remember her name) with Alex in the background, and his face is no longer bloody. I suppose he could've wiped it off but then in the next close up of him, the blood has returned!
copy of the movie/dvd and something to watch it on