Revealing mistake: Jeff tears a big chunk out of his face, but it never really bleeds out very much. It's pretty obvious that it's not just a layer of skin, you can see that there's a pretty big hunk of skin gone. At one point in the movie it's completely covered in blood, but only inside of the area of the tear. It should, at the very least, ooze quite a lot and drip something down his face, yet the area around the wound is always free from blood.
Plot hole: Out of all of the chains Troy had attached to him, one is hooked to his jaw which is near impossible to do as that would probably kill you and ripping it out would too, which is why Amanda would have placed it there. Jigsaw wouldn't have approved of it, and obviously there's no indication that Amanda had a medical profession, so how did she hook that chain to his jaw and even if she did, without killing him?
Continuity mistake: The third tape player is hanging from a string in some shots, but a cord in others.
Continuity mistake: The tear on Jeff's cheek briefly switches sides when he is holding the third card.
Revealing mistake: After Jeff shoots Amanda she falls to the ground. You can tell it is a dummy, just watch her arms and head.
Suggested correction: First of all, she doesn't fall to the ground. She stumbles after being shot and then slowly collapses to a seated position. There is also no dummy being used, as Shawnee Smith's face is visible in every shot of her until she dies.
Other mistake: Near the end of the film when Jigsaw has the tape player, the 'play' button is near the left side. But Jigsaw's finger is on the right side, not even close to the play button. Jigsaw presses on the right side where there isn't even a button, but the tape begins to play anyway although nobody pressed the actual play button.
Continuity mistake: The model of gun Amanda has when she shoots Lynn changes between shots.
Continuity mistake: Jeff's saw that he used to slit Jigsaw's throat is drenched in blood. Throughout the scene the blood stain gets shorter and longer.
Continuity mistake: There is a smear of blood on Jeff's right temple that disappears in the shot right after he drops the saw blade. It reappears in the very next shot.
Continuity mistake: When Jeff flips over the 3rd card he is holding it with his left hand by the left edge of the card, but when the scene (instantly) cuts away to a view of in front of Jeff you can see the he's holding it by the bottom (look at the way the card it bent).
Continuity mistake: The blood stains (streams) on Jigsaw's chest constantly change after Jeff slices his neck. Sometimes the only blood stain is a trail that goes directly down the side of his hospital gown, other times it's halfway down his chest. The shots constantly go back and forth, so it's not just the blood flowing down his chest.
