Continuity mistake: After examining Jigsaw, Lynn tells Amanda that he needs to go to a hospital. Amanda grabs Lynn's hair and pulls Lynn towards her to yell at her. In the shots of Amanda's face you can see that their foreheads are touching, but in the shots of Lynn's face their temples are the only thing that is touching. (00:37:25)
Continuity mistake: During Jigsaw's seizure there is a shot of Lynn when she's yelling at Amanda for help. In this shot she has several strands of hair that are across her face, but in the very next shot they are gone. She couldn't have brushed them away because her hands were on Jigsaw the whole time. (00:37:50)
Visible crew/equipment: There is one very quick shot when Lynn is asking Amanda for Ativan. In the one shot, look in the glass behind Lynn and see a boom arm. (00:37:50)
Continuity mistake: When Jigsaw is coughing up blood, the blood in the mask disappears between shots. (00:37:55)
Visible crew/equipment: When Jigsaw is having a fit, there is one very quick shot after Lyne tells Amanda to back off, that a boom mic is visible above her head. (00:38:00)
Revealing mistake: When Jigsaw is coughing up blood, the tube pumping the blood is visible. Look near his thigh. You can even see some red liquid oozing up. (Only visible in widescreen.) (00:38:20)
Continuity mistake: After Lynn looks for pills she runs back over and tells Amanda "Back off, back off", then takes off Jigsaw's oxygen mask and puts her hand on his face to keep his head to the side and you can see two drops of blood on her hand. The shot cuts to a closeup of Jigsaw and now there is no blood on her hand. (00:39:50)
Revealing mistake: When Lynn is inspecting the "reverse bear trap", the trap Amanda was placed in for the first movie, you can see a small orange light reflecting off a few surfaces, like Lynn's arm and the nearby table. This is the brightness level auto-adjustment light that is present on many handheld cameras, which the cameraman apparently forgot to cover or turn off. (00:47:20)
Continuity mistake: When Jeff finds the second box (after the freezer room) he takes the card and flips it over to see the picture on the back. In the closeup his thumbs are on the bottom corners, but then the shot cuts away to a view from his left and you can see that his left thumb is at the top left corner and his right thumb is as least halfway up the card (instant cut, no time to move his hands). (00:48:30)
Continuity mistake: When Lynn places down the drill there are 4 pieces of a broken mirror on the table in front of her. The 2 middle ones are standing straight up, but the outer ones are at various angles of slant. The next shot (a few seconds later) all 4 pieces are standing straight up and arranged very nicely. (00:49:40)
Plot hole: When John is painting the doll's face he looks down at a photo printout of Amanda, you will notice the bruising/scratches on the side of her face in the picture. Please take note of her hair, shirt and overall demeanor. Now think back to the first Saw when Danny Glover had Amanda in the interview room. The picture that John Kramer is looking at is a picture taken of her in "that exact" interview, this is strange however considering that the interview took place after she escaped the jaw splinter, so how does John have a picture of her from the future? (00:51:40)
Continuity mistake: The blood spot on Lynn's left sleeve (from when Jigsaw has a seizure) constantly changes size and shape throughout the whole movie. (00:51:40)
Continuity mistake: The tear in Jeff's face (after he gets stuck to the refrigeration machine) continually changes throughout the movie. It goes from oozing and bloody, to clean and almost normal looking several different times. There's no blood on his bathrobe, so he didn't wipe it off that way. That's a big enough tear to bleed a decent amount, so we'd see the blood if he wiped it off. (00:52:35)
Continuity mistake: When we see the Judge's tape for the first time it is completely horizontal. When Jeff reaches it, it is at an angle. (00:54:45)
Revealing mistake: During the "pig vat" sequence, as the pigs are being dropped into the grinder, in some of the shots from underneath the blades, you can see that the pigs are not falling directly into the blades, but rather, onto a sheet of glass right on top of them. (Look for the pigs to reflect in this glass.) (00:56:00)
Continuity mistake: When the tape player says "The key is among your son's possessions" Jeff is standing in front of the opening between the bars leading down to the ladder, and he takes a few steps towards the incinerator (his left). The screen cuts back to Jeff and you can see in the lower left-hand corner of the screen that Jeff is still standing in front of that opening between the bars. (00:56:10)
Continuity mistake: When Jeff sees the mini Jigsaw puppet on the tricycle, the handlebars are just red in one shot, but then they turn grey. (00:56:10)
Continuity mistake: In the "pig" room the string around the tape player suddenly disappears in the middle of the tape message. Jeff's right hand never changes position and the string was tied around the middle of the player, he would have had to move his hand to get it off. (00:58:00)
Continuity mistake: There is a far-away shot when the first pig comes out. You can see Jeff standing on the platform holding his left hand to his face, there's an instant cut to a close-up of Jeff, but now his right hand is held up to his face. (00:58:45)
Continuity mistake: In the 'Pig Vat' scene, the slide that the pigs slide on into the blades is clear with no pigs stuck on it. The pigs fall in one after the other with none getting stuck on the slide. However when the fourth pig drops onto the slide, you can see the a pig stuck on the slide and hanging over the edge of the slide. The next couple of pigs that fall don't knock another pig in and you cannot see the pig overhanging on the slide. (00:59:25)
Answer: It was too late for Adam to solve the game the way he was intended to- the key went down the drain, which Jigsaw actually didn't intend to happen. Adam's key was meant to be tied around his neck in such a way that neither him nor Lawrence would be able to see, and Adam would be allowed to go free and escape if he were to locate the key- which would only be possible if he looked at himself. The whole idea behind his puzzle was "looking at himself instead of others, for a change." The reason it went down the drain instead, was because of Amanda, who continuously made traps unsolvable. Instead of tying it around him like Jigsaw asked, she just tossed it on his chest, which defeated the whole purpose. Also, he was given a saw just as Lawrence was, as a much more violent plan B, another way he could save his own life.
That doesn't make sense because Jigsaw told Adam that the key is in the bathtub at the end of the movie.