Continuity mistake: Simone wraps the tube round her arm just as the camera does a flash change. When the camera shows Eddie briefly, you can see Simone in the background with her arm on the table and a knife to her elbow. However, less than a second before she was tying the tube. (00:03:50)
Revealing mistake: There is one shot of Simone cutting off her arm where you can see it is a fake arm. It's noticeable by the change in colour. (00:04:50)
Factual error: The license plate on the back of Jill's car does not specify the state. It only has the number listed and "Fairweather State" written at the bottom. While it's never specified what state the Saw films take place in, every U.S. state and Washington D.C. require vehicles to have a state-issued license plate on the rear of the vehicle, so it can't be a vanity plate. (01:00:31)
Continuity mistake: During the noose trap, William looks down the monitor's with Alan's pictures. We see a picture of Alan sitting in front of a fence, then William turns to look at Addy's monitor. In the next shot, William turns his head again to look at Addy's monitor. (00:38:10)
Audio problem: Simone's scream at the end of her game is the same as one used earlier in the scene. (00:06:00)
Revealing mistake: In the opening game, the same shot of the needle moving on the scale is used twice when Eddie drops some flesh onto the scales. (00:05:25)
Continuity mistake: When Hoffman goes to see Jill Tuck at the clinic, she unlocks her door and opens it. Camera changes and the hand she is opening the door with changes instantly. (00:20:00)
Continuity mistake: When the power goes out at Umbrella Health Corp, Williams puts the folder down. Camera cuts and he puts the folder down again. (00:24:00)
Continuity mistake: When William walks into the steam room, we see the tape player from William's point of view. The camera then looks at William and the tape player has rotated 180 degrees instantly. (00:50:25)
Continuity mistake: In the opening game, Simone's arm alternates from wet to dry depending on the shot. (00:03:30)
Visible crew/equipment: When Jigsaw says to William, that "success lies in the failure of your adversary", a boom mic can be seen reflected in the TV screen. (00:27:50)
Continuity mistake: At the very start, the position of the meat cleaver on Simone's table changes between shots. (00:03:40)
Revealing mistake: When Hoffman strikes the matches, he throws them in the petrol. However, if you look carefully you can see they are not lit when Hoffman throws them. (01:10:30)
Answer: The tools were chained to the tables, and there wasn't anything else they could've thrown down onto the scales.
erikvduyn