The voice behind Roz, the number 1 of the Child Detection Agency and the undercover secretary, is actually a man.

Boo's real name is Mary, this is only just visible on one of the drawings she is making while in Mike and Sulley's apartment.

When the monsters are on the scare floor to start scaring, they scare for a while, then it shows a blue monster quickly running out of the door saying that the kid almost touched him. When you see the monster running out. look closely because you can see the same poster that Sid has in his room in Toy Story.

Near the end of the film when Mike and Sully throw that Chameleon looking thing out of the door and into a trailer, you can see a Pizza Planet sign in the background. Pizza Planet was the pizza restaurant in both Toy Story films.

Most of the monsters that work on the scare floor are named after the good people who contributed to the making of the film.

Towards the end, just after Mike yells "I'm on the cover of a magazine.", he waves the magazine around (it's "Business Shriek"). On the back cover of the magazine, there is an ad for a monster-styled Macintosh computer. The layout of the ad resembles the layout of Apple ads; the Apple logo, and a slogan "Scare Different" that resembles Apple's "Think Different", are blurred but still recognizable, at the bottom of the ad. This is visible for less than a second, and is best seen by single-stepping the frames on the DVD. Why Macintosh: Steven Jobs is the CEO of both Apple Computer and of Pixar, the company that animated Monsters Inc.

Did you notice that Mike's mum looks like Roz? When they're doing the concert in the credits, after they do the play, Mike says, "What a night for my mother to be in the crowd", and you'll see Mike's mum.

Mike and Celia have dinner at Harryhausen's. This is a tip of the hat to Ray Harryhausen, the great stop-motion animator.

One of my favorite parts in the movie: When you first see Roz, she is reading "The Glob." Look closely at the headlines - they are hilarious. For example, "Three-Headed Baby Born - Parents Thrilled".

The makers of Monster's Inc. actually had many different ideas of what Sully and Mike would look like. Sully's first model had no hair and tentacles. Mike's first model had no feet and a moustache.

Mary Gibbs lends voice and personality to the enchanting little Boo and is actually the then three year old daughter of Pixar story artist Rob Gibbs and his wife Sue.

When Fungus is pulling down wallpaper behind Randall, just as he is preparing to enter his first door of the day, the wallpaper with the blue sky and small clouds is the same wallpaper from Andy's room in Toy Story.

When Randell is thrown into the door leading to the trailer, the trailer is off of "A Bug's Life" and also the Pizza Planet delivery truck is beside the trailer.

In the scene where Randall is being thrown through the door leading to the trailer you can see Nemo from "Finding Nemo" on the wall.

At the very end of the credits, there is a couple of lines that says "No Monsters were harmed in the production of this Motion Picture." Very cute.

Also in the end when Boo is handing her toys to Sully, besides Jessie, and the ball she hands him a clown fish. The fish is called Nemo, and it is from a new Disney and Pixar movie called "Finding Nemo", it is to be released in the summer of 2003.

Near the end of the film when Sullivan takes Boo back to her room and she is handing him her different toys, one of the toys she hands him is a Jessie doll. Jessie is the Cowgirl in Toy Story 2. If you look even closer you will notice that she also hands him the ball from "Luxo," one of Pixar's first animated shorts.

When Sully goes into one of the rooms, I believe he is looking for Boo's room, there is a set of bunkbeds, and if you look, under the top bunk, is a poster for Monsters, Inc.

After the Harryhousen's scene the voice of the CDA agent that says "building clear, proceed with contamination" is voiced by the director Peter Docter.

In the beginning, Mike and Sully are walking to work, and they pass the Hidden City Cafe and Pete's Barber Shop. These are both tip offs to the director. The Hidden City Cafe is his favourite restaurant, and the barber shop is named after him.