Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Saw
And this is one of the less dangerous traps.
Really, the concept of the movies. A man is killing people who don't appreciate their lives enough. Now, if you happen to have done any of the things that got characters in the films killed, and then are foolish enough to watch the movies, good luck sleeping. You'll be checking your closets for girls in pig masks for weeks.
The Razor Wire Maze. The cops on the scene noted that the wires cut so deep into the victim, that traces of stomach acid were found.
Dr. Gordon sawing his foot off. What made that worse was that Gordon's head was rational enough to wrap his leg in his shirt to cut of circulation and to bite on the cloth to withstand the pain. However, he wasn't rational enough to heed about three characters' statements that the game was over and nothing could be done anymore.
The ending, when Adam thinks he's killed Jigsaw, only to find that the man he killed also has a cassette player. Then while he plays it, and that awful music starts up, the corpse that was in the bathroom during the movie gets up. The piece of brain on the side of his head falls off, revealing it to be fake. He turns, looks down at Adam...and we realize we're looking at the real Jigsaw. He was in there with them the entire time.
Amanda in the pit of needles. And yes, this is the above picture. That trap is probably the only nonlethal trap in the entire franchise, but it still gives people massive shivers. Probably because...well, it's a pit of fucking needles. With a time limit where the safe in the room containing an "antidote" would close permanently if she failed.
Granted, this scene was nominated in the Scream Awards for "best mutilation scene".
The Furnace. Obi goes into a machine with two antidotes for the nerve gas the characters have been exposed to. When he grabs one, the device closes and the inside gets on fire, revealing it's a furnace. The characters on the outside are trying to get him out, but it's not working and he starts burning. They go to the other door of the furnace when a hand pushes itself against the glass. They break the glass and Obi pops out, but his face is all bloody and he dies.
It gets worse when you see the gas valve inside the furnace. By this time, though, the flames are burning so hot that Obi can't bring himself to reach through and turn it off.
Detective Matthews smashing his foot with the toilet tank lid to free himself, then snapping it backwards. And then walking through a hallway, causing it to break again. The sound effects don't help much.
The Rack. A crucifix which slowly broke the victim's arms, legs, and neck, by rotating them 180 degrees.
The Classroom Trap. The sounds were so excruciatingly horrific when he tried to break free of the chains pierced in his body.
Jigsaw's brain surgery. Regardless of whether you like the character or not, it's unbelievably nerve-wracking to watch a doctor cutting through someone's skull with a circular saw. He didn't even have any anesthetic!! Oh yeah, and they also used a drill on him, as if the saw wasn't creepy enough.
The Ice Shower, in which the victim is hung naked in a walk-in freezer and sprayed with cold water, causing them to freeze to death. This was probably one of the more forgettable traps, however if you've ever taken a shower when the water starts too cold and you remember the trap, it does make one a little uncomfortable. In context, this trap also seems harsher. to the victim who was only there because she fled the crime scene of the death of Jeff's son, in which she was the only witness. Of course it was cowardly and a pretty jerky move, but did she really deserve to die?
The Knife Chair can be described as "Push your face into the knives to hit a button that can free you." The result? The victim escapes and charges at Jigsaw, who sidesteps and makes him fall into razor wire. This actually gave Jigsaw the idea for the Razor Wire Maze in the first film.
The last of the would-be team traps can be a bit difficult to watch for anyone who particularly values their hands, especially due to how gratuitous it is with repeated cuts to the two last victims as they force themselves to shove their hands further onto sawblades, gradually slicing their arms in half the long way - on top of that, in an effort to shed five pints of blood each and hope they survive.
What happens to Strahm. The Walls Are Closing In, and there's nothing he can do about it. He tries to stop them with his arms, which gives us a lovely close-up of his arms collapsing like matchsticks. And the worse part is that he brought it on himself by not listening to the full cassette...
The Scale Trap. It's one thing to cut pieces of oneself, but making it a life-or-death competition between two people?
The Carousel Trap: Six people are chained to a children's carousel redecorated with Jigsaw's motif of doom, and every time it stops, a spring-loaded shotgun fires a bullet, killing the person in front of it. Meanwhile, the person being tested can push two buttons to stop a bullet from being fired, but only twice. And when they push the buttons, a screw comes straight down through their hand. And the whole time, the victims on the carousel are free to plead, scream, threaten, and cry as they realize that they haven't been deemed worthy to save by someone they viewed as a friend.
William's final test, in which the widow and son of one of his former clients have the chance to spare his life. The son decides that William doesn't deserve to live and triggers a rack of needles to pump him full of acid, dissolving his body from the inside out.
Saw 3D (a.k.a. Saw VII):
That goddamn Impalement Wheel. Imagine being strapped to a table that slowly raises you towards three sharp metal rods that will impale you through your eyes and mouth, utterly unable to do anything about it, except trusting in your friend to use a weight-lifting machine nearby long enough to stop the rotation, which will have spikes piercing his ribcage every time he does it. As a cherry on top the friend fails, and the audience gets to see what happens when the trap kills its victim! The 3D really makes it worse.
Jill's death, where we actually get to see the Reverse Bear Trap kill someone.
The death of Joyce. After Bobby fails his final test we're treated to the sight of her being cooked alive. The worse part is not only was the trapped intentionally designed so that it would fail no matter what, but she never did anything remotely wrong! She herself even encouraged people to live to the fullest, fully subscribing to John's philosophy. And she still suffered one of the most painful, arduous, and disturbing deaths in the whole franchise.
The ending. Dr. Gordon locks Hoffman in the bathroom from the first movie, with Gordon as Jigsaw and Hoffman as Adam. True, Hoffman had it coming, but damn.