Visible crew/equipment: Just as we see the flashback with Amanda, Jill looks at where Amanda stood, then turns to where John was stood and sighs. As she does, a boom shadow is seen to move across her hair. (00:23:15)
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)
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