Question: What would happen if William would stand on the other side of the cage? Then needles wouldn't stuck into him. Needles would hit the cage and start sprinkle acid in direction of mother and son, most likely hurting them. We learn from previous movies that Jigsaw planned his traps very carefully ,so he wouldn't allow that mother and son would hurt in any case.
Question: Why would John want Hoffman to be killed by Jill? What's wrong with him? I don't get it.
Question: Why did William cover the healthy people but did not cover the sick people?
Question: Here's an interesting thought; Debbie was provided with a small power saw and told that to prevent a pipe piercing her skull, she would have to get a key, which is revealed to be in William's side. What was to stop her from simply using the saw to cut off the spear on her chest? Couldn't she have cut it off her chest, and had the harness taken off later?
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.
Question: In the beginning scene where the two participants had to cut flesh in order to survive, what was to stop them simply putting other stuff on the scales instead of flesh, such as the heavy tools and knives and escaping that way?
Answer: The tools were chained to the tables, and there wasn't anything else they could've thrown down onto the scales.
Question: When John comes into Will's office, he explains that he wants to try an experimental procedure to help cure his cancer. It also has a very high success. But Mr. Easton denies him, claiming the cost would be substantial. He crumples up the paper and throws it away like he has run out of choices. Since John is a very wealthy man, why doesn't he just pay for it himself?
Chosen answer: The trap wouldn't have worked if William stood on the other side of the cage. When William walks towards the mother and son, you see a closeup of his feet stepping onto a pressure-pad that activates the trap. If William stood on the other side of the cage, the trap would never have turned on because the pressure-pad would not have been set off, and nobody would have died. Also, even though Jigsaw pre-plans his traps, there certainly are circumstances where the mother and son could have gotten hurt. One must remember, Jigsaw is insane, and it's shown repeatedly in the series that even though he intends to help people, he is not above sacrificing people or putting innocent people in harm's way to teach his subjects a lesson. (The most prominent examples being the mother and daughter from the original film and Joyce from "Saw 3D" who were innocent but placed in direct danger to be a motivation for the subjects).