Revealing mistake: After Dr. Lawrence cuts off his leg and is crawling towards the gun, if you look at his dismembered leg, you can make out the shape of his foot hidden beneath his ripped up slacks.
Revealing mistake: When Adam is searching Zep for the key to the chain once he has found the tape recorder watch Zep's stomach - he's breathing.
Revealing mistake: In Adam's flat just as he starts beating Jigsaw's doll (Billy) up, you can see that he's not actually hitting the proper puppet, but a cheap replica. You can tell by the red lines on it's face, and there is no red marks where it's mouth is.
Revealing mistake: In the scene when Zep arrives in the room and Lawrence is trying to grab at him, his foot is no longer leaving a blood trail.
Revealing mistake: The cut on Tapp's throat is visible a split second before his throat actually gets slashed.