Continuity mistake: Kerry wipes off the steamed up mirror and sees Eric in the reflection, she gasps and turns around. She looks back at the mirror and you can see that the hand wipe marks where she wiped the steam off are completely different. (00:11:45)
Continuity mistake: In the "Twisting Crucifix" device scene the tear on the man's face jumps from his right eye, to his left, then disappears, then reappears again throughout the shots.
Continuity mistake: The blood mark on Kerry's cheek changes several times. It's most easily noticeable when you first see her in the 'Angel' trap, and then a close up on her face at the 14:17 mark in the movie. (00:14:10)
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.
Continuity mistake: Amanda freaks out and pins Lynn to the wall after Lynn says "He doesn't even know you're there". Amanda's hand is around Lynn's neck, choking her. The screen cuts to Jigsaw very briefly (all he says is, "AMANDA!"), then back to Amanda, now Amanda's hand has moved up to being on Lynn's chin. Not only would moving her hand from Lynn's neck to her chin not serve any purpose, but the screen cuts happened too fast to allow for the hand movement. (01:14:25)
Visible crew/equipment: Just as Jeff and the judge walk out of the pig room, we see the judge walk through some plastic. When he walks through the camera is reflected on his back. (01:17:15)
Continuity mistake: The amount of blood on Jigsaw's skull changes drastically from thick dark red to thin almost translucent red. This is before Lyn clamps off the blood vessels and uses the alcohol to clear the area. (01:03:20)
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)
Continuity mistake: When Kerry walks into the room at the start of the film, her ID is twisted. Camera switches to a long shot and it's not twisted. (00:05:45)
Continuity mistake: When we first see Kerry in the Angel trap her arms are down by her side. The camera zooms out and now her arms are raised. (00:13:15)
Continuity mistake: When Jigsaw is saying about swallowing anti-depressants, his hand moves from his oxygen mask then back instantly. (00:25:10)
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)
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)
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)
Continuity mistake: When Rigg is telling Kerry that "That somebody is still out there", Hoffman can be seen in the background putting something in his jacket. Camera changes and his hand is nowhere near his jacket. (00:10:00)
Continuity mistake: When Kerry is in the Anglet trap, there is one point where her hand has almost grabbed the key out of the acid. The camera changes and her hand is nowhere near the key. (00:15:40)
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)
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.
Answer: Adam didn't just lose because he let the key get drowned. He had the two hacksaws and he broke his own in a hurry. And there was also the toilet lid that he could have used to smash his foot like Eric did in Saw III. Jigsaw never said that improvising or thinking outside the box was against the rules. So even if you wipe the key out of the equation, Adam still has at least two other ways to release himself from the chains.
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