Bill Murray was considered and tested for the role of Sulley, but the director, Pete Docter, said that when the filmmakers decided to offer it to Murray, they were unable to make contact with him and took that to mean "no".
The controls for the Monsters Inc. door mechanisms include a button that starts the process labeled "FIZT" - Fiz-T is in reality the latest software developed by Pixar Animation Studios to realistically render complex physical models - notably in this film to model Sulley`s fur and Boo`s clothing.
Sulley`s fur has over 2,320,413 hairs.
The last half of Chuck Jones`s 1952 classic Feed the Kitty (1952) cartoon is included scene-for-scene when Sulley thinks that Boo has been thrown in the trash compactor. Each of Marc Antony`s overdone reactions is echoed by Sulley against the window.
The cloud wallpaper from Andy`s room in Toy Story (1995) is seen briefly as one of the wallpapers that Randall uses to test his chameleon skills against.
One of the children`s rooms the monsters go into has a Paul Bunyan poster on the wall. Sid`s room in Toy Story (1995) had a Paul Bunyan poster in it (possibly even the same poster).
# # The slow-motion scene in which the scarers enter the scare floor parodies the arrival of the astronauts in The Right Stuff (1983) which was itself pastiched in Armageddon (1998/I) where Steve Buscemi played one of the pilots. In fact Randall`s position in the line is precisely where Buscemi himself was positioned in the original scene in "Armageddon".
Randall`s original name was Ned.
# # In the original draft of the script Sulley was not be a scarer but a worker. Also Mike was Randall`s assistant. In another draft, Sulley was Randall`s assistant.
Sulley`s original name was Johnson and he had brown fur.
# # John Lasseter made a five minute animated student film. called "Nitemare" (1979), which features monsters appearing in a child`s bedroom. The child finds out they mean no harm.
The Snowman describes the children in the Himalayan village as "Tough kids, sissy kids, kids who climb on rocks", a line taken from an old jingle for Armour hot dogs.
There are retro Disneyland posters in the Monstropolis travel store and some of the children`s bedrooms.
The restaurant that Mike and Celia are at is called the Harryhausen. This is an homage to Ray Harryhausen, the man who made the stop-motion animation monsters for films like Jason and the Argonauts (1963).
# # The Hidden Cafe is the name of a real restaurant in the San Francisco area which had been a favorite with Pixar`s animators since the early `90s.
When Sulley is about to say goodbye to Boo, Boo is trying to get him to play. She hands him a Jessie doll from Toy Story 2 (1999) as well as Nemo The Clownfish from Finding Nemo (2003). The yellow ball with the red star on the floor is the ball from the Pixar animation, Luxo Jr. (1986).
Randall Boggs is last seen in a trailer home. There is a Pizza Planet truck from Toy Story (1995) and Toy Story 2 (1999) beside the trailer, and the trailer and Pizza Planet truck were also featured in A Bug`s Life (1998).
The man inside the trailer is actually the simulated boy from the first scene. The mom is the same boy but with a "bun" placed on his head.
When Sulley shows the pile of trash (he thinks Boo is inside) to Mike, the sound the little lamp made in Luxo Jr. (1986) can be heard.
The artificial child featured after the beginning credits of the film looks remarkably like Andy from Toy Story (1995).
# # When Boo pulls on the stacked DVDs in Sulley`s apartment and they all come falling down, the DVD she`s holding can be seen to be A Bug`s Life (1998).
Pete`s Barber Shop is named for director Pete Docter. The Hidden City Cafe is a real restaurant in California, which is a favorite of Docter`s.
Disney/Pixar prepared a special trailer for Monsters Inc. to show before Harry Potter and the Sorcerer`s Stone (2001). Mike and Sulley play a game of charades in their apartment, with Sulley acting out "Harry Potter." Mike has difficulty solving the puzzle, some of his guesses being "Dirty Harry", "Harry Flowerpot" and "When Hairy met Sulley," (a reference to Billy Crystal`s starring role in When Harry Met Sally... (1989)). Eventually Sulley puts on round spectacles, sticks a paper lightning bolt to his forehead and sits on a broom with an owl on his arm, to which Mike ecstatically guesses "The Sound of Music". Sully gives up and walks offscreen as Mike finally guesses "Harry Potter" and the cut away to title cards noting that "Monsters Inc." is "Now showing at a theater near you. Really near you. Like, maybe, right next door." At the end of the trailer, it is Mike`s turn to act out a part, with a very bored looking Sully guessing it is "Star Wars" within seconds, much to Mike`s dismay.
# # The original teaser (where Mike and Sulley enter a room in "Outer Magnolia" instead of Outer Mongolia) was also specially made and features material which did not appear in the film. The scene from the trailer where Sulley tucks Boo into bed and says, "Don`t worry, I`ll protect you," does not feature in the film, either.
# # Boo`s real name is Mary, as shown briefly on one of the crayon drawings she shows to Sulley in the scene where Boo is going to sleep on Sulley`s bed. The actress who provided the voice of Boo is Mary Gibbs.
# # News leaked in early fall of 2001 that this movie would feature the first teaser for Star Wars: Episode II - Attack of the Clones (2002). Hundreds of Star Wars fans paid admission for the movie just to see the teaser and reportedly some left after seeing it.
# # This is the fourth movie to feature both John Goodman and Steve Buscemi and is the first of the four not to be directed and produced by Joel Coen and Ethan Coen.
Near the end of the credits a disclaimer states that "No monsters were harmed in the making of this movie."
The famous computer graphic of "The Teapot" can be seen on the table in Boo`s room.
In the background where the blob monster falls into a sidewalk grate, there is an art store called "Gallerie du Dominique". This store is named after Dominique Louis, an art director at Pixar.
On the scare floor leader board, the name immediately below Sullivan and Randall is Ranft, a reference to longtime Pixar writer Joe Ranft.
# # At Harryhausen`s Sushi Restaurant, employees shout, "Get a paper bag!" whenever somebody walks through the door. In Japan, it is customary for employees of any store to shout "irasshaimase!" (pronounced ee-rah-shai-mah-seh"). The monsters shouting, "Get a paper bag!" is a phonetic reference to this fact. There`s a similar Japanese reference in Toy Story 2 (1999) (see Trivia).
After Sulley says goodbye to Boo, he closes the closet door. When Boo jumps out of bed, she has grown 7% by the time she reaches the door. The programmers had to do this as she was too short.
# # John Goodman and Billy Crystal sometimes recorded their lines in the same room together, an unusual move for animated films, where actors more often work alone. Steve Buscemi and Frank Oz (Randall and his assistant Fungus) also recorded their lines together for the bathroom scene.
# # The ingredient list on the cereal that Sulley feeds Boo is as follows: Tentacles (includes s*ckers), sugar pods, gelatin, artificial flavor, artificial color (Yellow 53 & 54, Red 400, Blue 21, Plaid 16, Puce 30), salt, seawater, naturally occurring mercury, barium, sulfuric acid, lead, bile, blood, sweat, tears, zinc oxide, vitamins D & F, anemone, brine shrimp, coral, plankton, deadly pufferfish, depleted uranium (to preserve freshness).
The octopus behind the bar in Harryhausen`s restaurant has only six legs. This is a reference to It Came from Beneath the Sea (1955), a film in which Ray Harryhausen created an octopus with six arms due to budget restrictions.
# # In the simulated bedroom used for training the letters of the alphabet can be seen as a border at the top of the walls. For some reason the letter J is backwards.
The Snowman is modeled after the Abominable Snowmonster from the TV special Rudolph, the Red-Nosed Reindeer (1964) (TV).
# # Towards the end of the movie, Mike opens a package with a magazine featuring Sulley and Mike on the cover. On the back is a full page advertisement for a computer system with tagline at the bottom "Scare Different..." Meanwhile, the new slogan "Think funny" appears all over the scare floor after the change in the corporation. These are both nods to Steve Jobs, CEO of Pixar and Apple (which had the "Think Different" ads).
In early drafts, the character of Boo was written to be six years old. The writers decided to make Boo younger because it would make her more dependent on Sulley.
About 3:26 into the movie, when the simulation is ended and the monster reaches for a knob on the control panel to review the videotape, just below and to the left of the knob is a little indicator which reads "510-752-3000", which is Pixar`s phone number.
All of the digital displays in Monstropolis (Sulley`s clock radio, scare station consoles, "Days Without An Accident" sign) are nixie tubes, a neon digital display technology from the 1960s.
# # At the very end, when Mike is talking to Sulley on the Laugh Floor, just before showing him the rebuilt door, a giant version of a pop-up clown toy in Andy`s room from Toy Story (1995) can be seen behind them.
George Sanderson (the monster who keeps getting caught by the CDA for "2319" emergencies) is the monster who was supposed to be the protagonist for the original Monsters, Inc. concept - a bumbling, inept monster who couldn`t scare anyone, `til a timid girl, put upon by her brothers, teaches him how to be scary. George in the final version is even the same color and monster type in the original storyboards.
When Mike and Sulley emerge from the straw house on the beach, the Toy Story (1995) cloud is visible in the sky.
# # In the ending sequence when the monsters make children laugh instead of cry, one monster on the factory floor can be seen carrying a sledgehammer and a watermelon - a clear homage to the comedian Gallagher, who popularized that particular gag.
In an early draft, Sulley was supposed to be a lowly helper. In fact, a quite long storyboard had been made of this original plot as shown in the DVD.
Sulley`s big armchair in his apartment has a hole in the back to let his tail through.
When Boo is in the bathroom stall she "sings" two songs. The first one is to the tune of Beauty and the Beast (1991), another Disney movie. The second one is to the tune of "One Love", from Snow White and the Seven Dwarfs (1937).
When Sulley and Mike are walking to work, they go pass "Tony`s Grossery".