- The first scene can be frightening to anyone afraid of the idea of monsters hiding under their bed, specifically the shot with the glowing eyes under the boy's bed. This is later averted, however, when the whole thing is revealed to be a simulation gone wrong.
- Overlapping with Paranoia Fuel, Randall uses his invisibility to absolutely chilling effect against Sulley. Since he's invisible to the audience too, we're held up in suspense once he disappears and starts scampering 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 Waternoose and thinks he's lost him...and then 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 Sully 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 don't find it funny due to his over-the-top reactions, Sully 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.
- The Scream Extractor, a machine that clamps over the mouth of the restrained victim and forcibly extracts the scream. It's demonstrated that it extracts the breath as well as the screaming. Had Sulley and Mike been unable to save Boo, it was Randall's and Waternoose's stated intent to have the Scream Extractor either leave her and other children) a dead, withered husk or worse, kept to low power, in which they would have been trapped in it indefinitely having the scream drained from them 24/7.
- According to the DVD Commentary, the scene where Sulley rescues Boo, the walls to the corridor leading to Waternoose and Randall's secret lair, were supposed to 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.
- During the final confrontation with 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.
Waternoose: This has gone far enough, James!
- There's also the chase scene in general - while his design as a crab/spider monster has never been the most comforting thing, 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 Sully, with some of his legs briefly running along the wall to boot, can be a terrifying sight for anyone who's 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, Waternoose suddenly appears through the bedroom door.
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 Sully) I'll kidnap a thousand children before I let this company die! And I'll silence ANYONE WHO GETS IN MY WAY!!
(he backhands Sully hard enough to knock him to the floor, then seemingly grabs Boo with the clear intent to strangle her to death.)
- Though Boo "rampaging" Mike and Sulley'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.
- In the second DVD, there is a feature of the original treatment for Monsters Inc. In one particular scary scene, Boo is hiding from Sully's landlady, whose eyestalks can stretch and slither about like snakes.
- In another scary scene, Boo runs away from Sully 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 Dwarves, inanimate objects suddenly come alive! Trash cans, street lights and even sewer grates suddenly grow eyes and mouths with sharp teeth and start closing in on her.
- While on the run with Boo, Sully 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 zero warning.
Nightmare Fuel / Monsters, Inc.