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)
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: 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)
Continuity mistake: When William sees the way forward, he puts his hand on the glass. There is no blood on the glass from the previous shot, and in the next shot, when he tells Addy to be careful, the blood is back. (00:39:20)
Continuity mistake: When Hoffman says to Amanda "Are you sure about that?" his mouth is right next to her ear. Camera cuts and it's a lot further away. (00:44:10)
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)
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: The amount of Petrol that Hoffman chucks over the FBI lab, Perez, and his boss, is more than what could be in the single container we are shown. (01:09:00)
Factual error: We see Hoffman has to use pliers and force to remove Strahm's hand from the grill. However, since the hand is freshly severed, rigor mortis would not have set in, and he should have been able to remove it with ease. (01:09:30)
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)
Revealing mistake: When William is running at the end, there is already a blood trail on the floor. Clearly from another take. (01:15:10)
Continuity mistake: We are shown a clip at the end of someone putting the reverse bear trap on Amanda in Saw. However, the device is not the same one as seen in Saw. Note the mouth section. It is a lot thinner than in Saw. (01:17:50)
Continuity mistake: Jill opens the 6th envelope to show Hoffman. When she does, the envelope instantly vanishes from her hands. (01:18:25)
Chosen answer: It's possible, but unlikely. 1) She was under great distress and might not have thought of that. 2) It would be easier (and more importantly, quicker) to cut through Easton's soft skin than the spear. 3) There is a good chance that tampering with the spear might have made it go off.
TedStixon