Continuity mistake: Gibbs smashes the glass at the junkyard with a shotgun. The smashed glass changes between shots. (01:26:20)
Continuity mistake: Bobby gets stabbed when trying to save the one person. However when he is trying to save his wife, the puncture marks are constantly disappearing and reappearing.
Visible crew/equipment: In the first shot at the public trap, you can see a camera crane reflected in the mirrors.
Continuity mistake: When Dr. Gordon cuts his leg off in the first Saw film and leaves the bathroom, he leaves a big trail of blood. But in every movie after that you never see any type of blood trail at all.
Answer: Dr. Gordon from the 1st movie, and Ryan and Brad from the trap in the beginning of this movie.
derrick g