Plot hole: Det. Kerry says at the scene of Paul's trap, "He had two hours." There is no way she could have known that. The clock simply said 3:00 and the tape specifically says "you have until 3 o'clock or this room will become your tomb". No way to know that's two hours after the fact. (00:17:30)
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.
Continuity mistake: When Alison gets the gun from Zep and aims it at him, the gun is in her left hand. In the next shot it's in her right hand, and then it moves back to her left hand again. This is not an artifact of changing camera angles, you can clearly see the different hands holding the gun. (01:20:30)
Visible crew/equipment: In the scene where Adam walks around his apartment with his camera (because the lights were out) the filmmakers put lights in the set so the actors wouldn't walk into walls, and also letting the audience see what's actually happening. In the movie, though, there are supposed to be no lights on at all. However, just before Adam opens the closet door with Jigsaw in it, you can see the reflection of one of the set's lights on the top of Adam's camera.
Factual error: The Swedish subtitlers made Amanda's situation even more tragic, incorrectly translating her dead cellmate as her dead soulmate.
Continuity mistake: When Larry is desperately trying to reach for the cell phone, he uses the box that it came in. When that doesn't work he throws it off to the side (his left) but when we see it again the box is back where it originally was (on his right).
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.
Visible crew/equipment: After the first call when Dr Gordon gets on the cell phone, a boom mike shadow is visible on the bathroom door. (00:10:00)
Plot hole: Jigsaw is lying on the ground with a gun in one hand, and a tape recorder in the other; the tape recorder is removed, leaving his hand empty. If both of his hands were occupied/exposed, he would have had no way of depressing the button on the remote control to shock the prisoners. As seen at the end, when he shocks Adam the final time, the control is in his hand, not hidden anywhere else on his body.
Continuity mistake: When Dr Gordon begins to saw his foot off, the blood seen covering his neck and top disappear in subsequent shots. (01:26:40)
Continuity mistake: In the scene where. Lawrence and Adam find the 'X' on the wall, there is a continuity error. Right after they find the 'X', the lights are turned on and there is the shape of a square on the wall (the cavity where the box is hidden). Before they find the 'X' there is no box or any dirty lines where the cavity is. (00:54:00)
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.
Visible crew/equipment: You can see the shadow of the camera on Dr. Gordon's sleeve when he is talking to Diana sitting on her bed. (00:34:20)
Continuity mistake: When Dr. Lawrence opened his envelope he got a key in it. When he tried it on the lock on his chain and it failed to open, Adam then asks to try it. Right when Adam asks for it, he puts his tape and envelope down separate, but when reaches for his tape again, it has ended up inside the envelope. (00:07:50)