Continuity mistake: When Adam and Gordon are talking in the beginning, Adam's hair moves between shots. (00:03:40)
Continuity mistake: Dr. Gordon rips open his envelope near the start. When he does he rips it with the "A" in "Lawrence" still visible. Camera cuts and the rip has moved down to take off half of the "W". (00:06:45)
Continuity mistake: When Dr. Gordon picks up his tape, the way he holds it changes instantly. (00:06:50)
Continuity mistake: Dr. Gordon empties his envelope into his hands in an extreme closeup. In this shot you can see the tape is not sticking up. Camera changes and the tape is now sticking up. (00:06:50)
Continuity mistake: Dr. Gordon gets a key in his envelope. The way he hold it changes instantly. Note the straight edge. (00:07:10)
Continuity mistake: When Dr. Lawrence opened his envelope he got a key in it. When he tried it on the lock on his chain and it failed to open, Adam then asks to try it. Right when Adam asks for it, he puts his tape and envelope down separate, but when reaches for his tape again, it has ended up inside the envelope. (00:07:50)
Continuity mistake: When we first see the heart on the toilet, the lid is on upside down. When we see Adam look at it, the lid is on the right way up. (00:12:35)
Continuity mistake: When Adam retrieves the bag with the saws from the toilet, he places it on his right side. At one point you can see that there is nothing on his left side, but the next shot shows Adam grabbing the bag from his left side and tossing it into the tub. (00:14:00)
Continuity mistake: When the victims first find the saws and are vigorously trying to cut the chains: The wide angle of Larry sawing, shows him cutting at the chain. Close up he is cutting the padlock. (00:14:20)
Continuity mistake: We see Adam on Dr. Gordon on the screen that Zep is watching. By Adam's foot there is nothing, yet when we see Adam, there is a piece of glass. (00:30:00)
Continuity mistake: When we see the bathroom again after we hear about Amanda, the clock is at 11:35. When Adam breaks the glass, just a few continuous minutes later, the time is 12:20. (00:30:00)
Continuity mistake: When Dr. Gordon gets out of Tapp's car and is talking to him at the car window, the amount of shirt sleeve showing under his jacket changes between shots. (00:42:00)
Continuity mistake: Tapp is watching the Amanda tape. Jigsaw says "look" and then Tapp rewinds the tape for 2 seconds. He presses play and Jigsaw says, "Look around" He should have said the word "mate" at that point. (00:43:40)
Continuity mistake: In the scene where. Lawrence and Adam find the 'X' on the wall, there is a continuity error. Right after they find the 'X', the lights are turned on and there is the shape of a square on the wall (the cavity where the box is hidden). Before they find the 'X' there is no box or any dirty lines where the cavity is. (00:54:00)
Continuity mistake: When Larry looks at the picture with Zep at the window, from one angle the picture is all crumpled but in the first person view, it's smooth. This changes several times. (01:18:40)
Continuity mistake: When Ali is pointing the gun at Zep, she is either holding it in her left hand or two-handed at one point. This is not to be confused with when the gun swaps hands. (01:20:15)
Continuity mistake: When Alison gets the gun from Zep and aims it at him, the gun is in her left hand. In the next shot it's in her right hand, and then it moves back to her left hand again. This is not an artifact of changing camera angles, you can clearly see the different hands holding the gun. (01:20:30)
Continuity mistake: When Alison is pointing the gun at Zep, Zep's position in relation to the bed changes instantly. (01:20:50)
Continuity mistake: When Dr. Gordon is trying to get the phone it is just mm away from the box. When the camera changes, it's a good few inches away from the box. (01:25:05)
Continuity mistake: When Dr Gordon is going crazy, he throws the box to his right, but in the next shot it's on the left, then on the right again. (01:25:50)
Answer: Amanda was supposed to put the key around Adam's neck rather than just on his chest. If she had done so as instructed by Jigsaw, he would've been able to unlock his shackle and leave the bathroom. Adam was a voyeur, the irony being that if his key had been placed correctly around his neck, all he would've had to do would be to look around to find it. Adam's tape states, "what do voyeurs see when they look into the mirror, " so, again, it's a hint that all Adam would've had to do was look at himself. I noticed as well, Jigsaw says, "the key to that chain is in the bathtub." /IS/ in the bathtub. Not /was/. So Jigsaw probably thought Adam could still get out. He says, "so many people are ungrateful to be alive. But not you. Not anymore." So it's like, 'I have taught you this lesson, now you can go free because now you'll appreciate your life unlike you did before'.