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)
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