Visible crew/equipment: In the electricity trap, after a brief close up, it snaps to a view of the whole room, you can see the boom mic lifting up and actually see outside of the set.

Continuity: Throughout the movie, the clocks show incorrect time and at times changes from 8:20 to 18:20 and the countdown clock shows wrong sequencing.

Deliberate "mistake": When Agent Strahm is in his head box trap screaming, there is a lot of flash-cutting, including a shot of an outtake of the actor smiling with a towel.

Audio problem: When Detective Hoffman was shown captured by Jigsaw to be recruited into his 'game', Jigsaw introduces the notion of not liking being given credit for work that's not his. It appears as if he is speaking based on jaw movement but no sound comes out.

Continuity: When the Realtor is getting out of the final room, the door is left open and the FBI agent is talking to her. The nail bombs never go off, although the counter never stopped.

Plot hole: There is no way that the grated doors in the second part of the sewer tests would have protected their occupants from a nail-bomb explosion that was powerful enough to pulverize Charles's body. The nails and debris would have been propelled through the doors and fatally impaled whoever was inside.

Other: When Agent Strahm first starts investigating, he uses the FBI computer to look up Seth's name. He is heard typing many more characters, very quickly, than actually show up in the 'search' field on the screen.

Continuity: After Ashley is decapitated in the collar trap, we see her body later on from the view of the hidden cameras. But by the time we see her corpse, the nail bombs have already gone off and should have caused some damage to it or the room, yet neither is visible or present.