- The first scene can be frightening to anyone afraid of the idea of monsters lurking around in their bedroom at night, as evident in the shot of a monster's glowing eyes under the boy's bed. This is eventually averted when the whole thing is revealed to be a simulation gone wrong by virtue of it turning into a hilarious Epic Fail of the Scarer.
- Overlapping with Paranoia Fuel, Randall uses his invisibility to absolutely chilling effect against Sulley. Since he is also invisible to the audience, we are held up in suspense once he disappears and starts to scamper all over the place. An especially effective moment is when Sulley and Boo are hiding on the scare floor... and Randall materializes right beside them.
- In another scene, Mike is trying to escape from Randall. He ends up in a hallway next to a portrait of Mr. Waternoose and thinks he has lost him... and then Mr. Waternoose's portrait suddenly blinks. It's Randall, blending into the colors of the portrait. Needless to say, the audience's reaction mirrors the one Mike has when he turns around to see Randall standing behind him.
- The scene of Sulley being strangled by an invisible Randall. It's mixed in with the comedy of Mike being completely oblivious, but hearing his breath slowly leak out as well as the dramatic music is very disturbing. Especially considering the fact that you can see his neck getting crushed.
- When the monsters harvest screams from little kids, a monitor displays how much screams they have collected with Celia announcing such events in a deadpan fashion. Strangely similar to the telescreen. Creepy.
- On the DVD, there was an Easter Egg that showed the giraffe used to measure height on Boo's wall moving, then peeking around her door to look straight at the camera.
- On the DVD, on the second disc in the "Humans Only" Menu, watch the production tour all the way through. You will then be treated to a bunch of doors, each containing an Easter Egg. One of them is Sulley scaring the simulation room kid.
- If you do not find it funny due to his over-the-top reactions, Sulley mistakenly believing his beloved Boo is in the trash disposal machine is this as poor Sulley honestly believes Boo is being horribly mangled to death.
- Randall's sinister entrance when he opens the door to the Himalayas and Mr. Waternoose's statement to Sulley and Mike, "It's yours." Mr. Waternoose's pose after he pushes Sulley and Mike out the door is quite intimidating; Sulley quickly tries to run back inside, but Mr. Waternoose closes the door and the room has disappeared by the time Sulley opens it.
- The CDA can be pretty intimidating, at least in their first few scenes. The suits don't help, making them look like red-eyed, rubber aliens, it's enough to make you uneasy if you're a kid watching this film, though as the movie goes on, the menacing aura fades.
- They first show up when George gets a sock on his back, storming through Monsters Inc. into the Scare Floor in a matter of seconds after the alarm was set off, some even entering through the windows above. They rush through the place searching for the "toxic" item, managing to scare a few employees in the process, one even seeing fit to hide under the table. Then when they finally find the sock, they see fit to cover it up and nuke it. But they aren't quite done, as they then shave George and rip a bandage off of him, likely to keep any of the alleged toxins from staying on his body. Maybe it's the sight of a banage getting torn off, maybe it's how George looks without fur, but something about the scene can make it difficult to sit through if you're squeamish.
- Their second scene at the restaurant isn't any better. The place is in a riot and they show up to contain it, almost looking like aliens (again) swooping down and capturing people. Yeah, it's their job, but the scene certainly does a good job putting you on edge. Then there's the way they decontaminate the entire restaurant, which looks, for a third time, like something out of a sci-fi horror film.
- Even worse, in the original cut of the film, they deal with the situation by nuking the restaurant.
- The Scream Extractor, a machine that clamps over the mouth of the restrained victim and forcibly extracts the scream. It is demonstrated that it extracts the breath as well as the screaming. Poor Fungus ends up with his color drained and his lips swelled up and he is almost out of breath. Had Sulley and Mike been unable to save Boo, she and millions of other kids would have ended up looking like him. According to the DVD Commentary, the scene where Sulley rescues Boo, the walls to the corridor leading to Randall's secret lair, were supposed to be lined with cages, implying that they were ready to take the operation full scale as soon as possible. The idea was scrapped because the scene where Boo strapped to a chair was disturbing enough.
- The scene where Boo is strapped to the Scream Extractor. She tries fruitlessly tugging her hands out of the restraints before crying out for Sulley and her mommy. Bear in mind that she spent the whole movie happily wandering through Monsters Inc. unaware that she was in a monster world. Now she realized she was in danger and couldnt do anything to save herself.
- During the final confrontation with Mr. Waternoose, Sulley runs away with Boo into the Scare Simulator room, and attempts to lock the door shut with a piece of a metal pipe. Thanks to some pretty impressive lighting, Waternoose slowly bashing his way in actually makes him look quite threatening.
- There is also the chase scene in general - while his design as a crab/spider monster has never been the most comforting thing, Mr. Waternoose has never been shown making any sudden or drastic movements in the way many are freaked out of those animals over. The sight of a furious six-legged monster rapidly scuttling down a hallway after Sulley, with some of his legs briefly running along the wall to boot, can be a terrifying sight for anyone who is creeped out by the way crustaceans or arachnids can move.
- Then just when it seems Sulley has returned Boo to her bed safe and sound, Mr. Waternoose suddenly appears through the bedroom door.Waternoose: This has gone far enough, James!
Sulley: She's home now! Just leave her alone!
Waternoose: I can't do that! She's seen too much! You both have!
Sulley: It doesn't have to be this way!
Waternoose: I have no choice! Times have changed! Scaring isn't enough anymore!
Sulley: But kidnapping children?!
Waternoose: (Shouting, slowly standing taller over Sulley) I'll kidnap a thousand children before I let this company die! And I'll silence anyone who gets in my way!
(he backhands Sulley hard enough to knock him to the floor, then seemingly grabs Boo with the clear intent to strangle her to death.)
- Just the fact that had Sully failed to hide Boo in time when Mr. Waternoose broke through and trick him into strangling the dummy, Death of a Child would have been Played Straight.
- Though Boo "rampaging" Sulley and Mike's apartment is quite hilarious, there's a brief bit where she "corners" Sulley. Her eyes were totally focused on him and when she tosses the CD's she was holding aside, she keeps looking at him and keeps walking. She almost looks zombielike as she does this, right down to her hands reaching out.
- While on the run with Boo, Sulley is forced to give a demonstration of his scaring technique, letting us see just how this lovable, cuddly guy came close to getting the most screams in the company's history as he gives a ferocious roar straight to the camera. Even worse for Boo having to see her Kitty turn into a monster with absolutely no warning. Keep in mind that, other than a few comedic demonstrations throughout the movie (his training with Mike and showing Waternoose the "Jump and growl"), we had never seen Sulley scaring children until now.
- In the second DVD, there is a feature of the original treatment for Monsters, Inc.
- In one particular scary scene, Boo (then called Mary) is hiding from Sulley's (then called Johnson) landlady, whose eyestalks can stretch and slither about like snakes.
- In another scary scene, Boo runs away from Sulley after finding out he knows her door is fixed (which he broke earlier in the story) but did not tell her. Eventually, she becomes lost and, in a moment straight out of Snow White and the Seven Dwarfs, inanimate objects suddenly come alive! Trash cans, street lights, fences and even sewer grates suddenly grow eyes and mouths with sharp teeth and start closing in on her.
Nightmare Fuel / Monsters, Inc.