Mary Gibbs was so young that it proved difficult to get her to stand in the recording studio and act her lines. Instead, they simply followed her around with a microphone and cut Boo's lines together from the things she said while she played.

It normally took 11 to 12 hours to render a single frame of Sulley because of his 2.3 million individually animated hair strands (Total number of hairs: 2,320,413).

Highest-grossing animated film released to its date.

John Goodman pushed for Steve Buscemi to voice the villain Randall.

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.

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 (1971), "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 (1965). Sully gives up and walks off-screen 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: Episode IV - A New Hope (1977) within seconds, much to Mike's dismay. Coincidentally, Disney would acquire Lucasfilm (the production company behind the Star Wars franchise, among others) for $4.5 billion in 2012, a year before the release of prequel Monsters University (2013)..

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.

Billy Crystal was originally offered the role of Buzz Lightyear in Toy Story (1995) and he declined, which he later regretted after seeing the film itself, as it would've been a great opportunity for him. They would later promise Crystal a future role in a Pixar film that they would tailor to his talents. Crystal told them to "do what's best for your movie and don't forget me when something good comes around". Later in the late 1990s/early 2000s, Crystal's wife received a phone call from John Lasseter, who told him "Mr. Lasseter would like to speak to you", allowing him to voice Mike in Monsters, Inc. (2001).

Jennifer Tilly, who plays Celia Mae, was married to Sam Simon who was one of the creators of The Simpsons (1989). She raved to the Pixar crew about a script she read written by a Simpsons director for an animated film. The Director was Brad Bird and the script was for The Incredibles (2004) which became a Pixar film 3 years later.

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.

In the first scene, one of the toys on the boy's bedroom shelf is the toy plane that hung from the ceiling and caused Buzz to "fly" in and as Mike and Sully go through the scare floor, the rolling clown, from Toy Story (1995) can be seen in the background. Also, when Randall is practicing camouflaging into backgrounds of walls, one of the images given to him is the wallpaper Andy had in his room.

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.

The scoreboard at the scaring contest consists of names of Pixar staff members.

When Sully greets Ted (the monster so big we only see the lower half of his body), Ted was originally supposed to roar like Godzilla. The filmmakers asked permission from Toho (Godzilla's film studio) to use a Godzilla roar, but Toho turned them down, so Ted responds with a chicken cluck instead. In one of the credit bloopers, though, he was revealed to be a dinosaur - Rex, from Toy Story (1995) - auditioning for a role in the movie.

The restaurant that Mike and Celia are at is called Harryhausen's. This is an homage to Ray Harryhausen, the man who made the stop-motion animation monsters for films like Jason and the Argonauts (1963). Also, the octopus behind the bar in the restaurant with only six legs is a reference to It Came from Beneath the Sea (1955), a film in which Harryhausen created an octopus with six arms due to budget restrictions.

The spin off short film Mike's New Car (2002) was originally planned as a scene in the film. It was removed from the film and made as a short, being the first Pixar short film to have dialogue.

The ingredient list on the cereal that Sulley feeds Boo is as follows: Tentacles (includes suckers), 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).

In the German dubbing of the film, the Abominable Snowman speaks the Swabian dialect, which is mostly spoken in southwestern Germany, and makes a reference to wishing he had been banished to the Swabian Alps where he has friends.

Bob Peterson, the movie's story supervisor, provided the temporary voice of Roz, the green secretary, during production. The nasal, sing-song voice proved to be such a success that they kept it in the final film.

There are retro Disneyland posters in the Monstropolis travel store and some of the children's bedrooms.

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).

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.

The animators considered giving Sulley tentacles instead of legs at one point, and glasses at another. However, they decided to use legs because they believed the audience would concentrate more on the tentacles than Sulley's face. They also considered making Mike armless with only legs.

The Abominable 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.

Sulley's big armchair in his apartment has a hole in the back to let his tail through.

In the original draft of the script, Sulley was not to be a scarer but a worker named Johnson with brown fur. In fact, a quite long storyboard of the Sulley-as-lowly-helper is shown on the DVD. Also, Mike was the assistant of Randall (who was named Ned in the first version). In another draft, Sulley, originally called "Barrymore", was Ned/Randall's assistant. 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.

Boo's teddy bear is the same bear as the one seen on the shelf in the simulator bedroom.

According to the commentary, when Mike is on the run from Randall, he hides in a room but relinquishes himself when he turns and sees Randall in a window, staring at him and beckoning. It is only when Mike gives himself up that he realizes Randall was in the opposite room, looking in the mirror and picking his teeth.

The first Pixar film to tease Pixar's next film in a way, by having some sort of cameo based off it, as well as the last film to cameo someone or something from Pixar's previous film.

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". His younger brother Joel Murray would later go onto voice Don Carlton in the film's prequel Monsters University (2013) 12 years later.

According to the film's credits, no monsters were harmed in the making of the film.

The famous computer graphic of "The Teapot" can be seen on the table in Boo's room.

On the DVD bonus features, the three ads at the end of the company play, "Put That Thing Back Where It Came From, Or So Help Me!" are for Tony's Grossery (seen earlier in the movie when Mike and Sulley pass it), Pixar Shorts ("We've got the important things covered") and Pete's Barber Shop (specializing in/selling Claw Wax, Scale Polish, and Mange Management).

At one point, when Sully got his final design, he was going to wear glasses. But the glasses were taken off in order to show more of his eye expressions.

When Fungus, overjoyed of no longer having to work for Randall, puts the mustache glasses on at the end of the movie, he looks very similar to the way his voice actor Frank Oz looked in the 80's.

Sully is named after former Texas A&M University president Lawrence Sullivan "Sully" Ross.

When Sulley and Mike are walking to work and pass "Tony's Grossery", the items on sale include Mangle Fruit, Bilge Berries, and Blood Oranges (a real kind of orange).

At the beginning when Mike and Sully are walking to work Mike says "you've been jealous of my good looks since the 4th grade...", but the prequel Monsters University (2013) tells us Mike and Sully didn't actually meet until college.

The idea for the film was first conceived over a lunch between John Lasseter, Pete Docter, Andrew Stanton and Joe Ranft in 1994 during the production of Toy Story (1995).

Randy Newman's song "If I Didn't Have You" finally netted the composer an Academy Award after 16 nominations.

Boo speaks giberish the whole movie, but seems to pronounce Mike Wazowski perfectly.

The "Hidden City Café" is the name of a real restaurant in Point Richmind Ca which had been a favorite with Pixar's animators, including director Pete Docter, since the early '90s. Pixar was originally located in Point Richmond Ca

EASTER EGG: The Human World, that Randall is tossed into in, has used the same set from "A Bug's Life " (1998) with the trailer and the Pizza Planet Truck from the movie Toy Story (1995) is parked.

James Coburn's last film before his death 1 year later.

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.

When Sully throws Randall into a room, if you're not distracted by Mike, then you will see a model of Nemo from Finding Nemo (2003).

The first Pixar feature release not to be directed by John Lasseter.

'2319' might refer to the 23rd and 19th letter in the alphabet: WS. WS stands for White Sock, because a white sock is the first human object to be destroyed by the CDA.

The green shield that the CDA uses to decontaminate the restaurant Harryhausen's is similar to the Martain protective shield from the 1953 production of "The War of the Worlds."

Originally intended in release on Thanksgiving in 2001 like the previous 3 Pixar Films, but was pushed forward 3 weeks to November 2nd to avoid clashing with the release of the live action film Out Cold (2001) by Touchstone Pictures on that same day.

Pixar Animation Studios' 4th feature film. As well as the first Pixar film to be released in the 21st century.

The only Pixar film of the 2000s to have bloopers.

Unlike previous Pixar productions, each of the main characters were assigned their own individual animator. John Kahrs did Sulley, Andrew Gordon worked on Mike and David DeVan did Boo.

Computing power is measured in rendermarks. Toy Story 2 (1999) required 1.1 million. Monsters, Inc. (2001) took 2.5 million.

As of January 2016, this is Pete Docter's only G-rated feature film. His other films, Up (2009) and Inside Out (2015) have both received PG ratings.

This is Pete Docters only Disney/Pixar film that didn't win an Academy Award for Best Animated Feature. Up (2009) and Inside Out (2015) have both won, but Monsters, Inc. (2001) lost to Shrek (2001). This is also one of only two Pixar films to be nominated for the award without winning it, the other being Cars (2006).

The Luxo Jr. ball is on the floor when Sulley goes through Boo's door for the first time.

Not only is the Pizza Planet truck by the trailer where Randall is getting beat up, but also the trailer that he is in resembles the same trailer from A Bug's Life (1998). So if the Pizza Planet truck is there too, than it made the same picture from A Bug's Life (1998) where the Pizza Planet truck is sitting by the trailer.

In the movie, there are several hidden Easter eggs referencing to what was their next film, Finding Nemo (2003). First, At the Harryhausen's restaurant, behind the octopus chef, there is a painting of Nemo on the wall. Second, when Sulley throws Randall into a bedroom, a statue of Nemo can be seen on the wall into the bedroom. And last but not least, when Boo hands Sulley some of her toys, she hands him a Nemo toy.

The first Pixar film to win an Oscar, being Best Original Song. It was nominated for 3 others, Best Animated Feature, Best Original Score, and Best Sound Editing, but lost them to Shrek (2001), The Lord of the Rings: The Fellowship of the Ring (2001), and Pearl Harbor (2001).

The only Pixar film directed by Pete Docter not composed by Michael Giacchino, who composed Up (2009) and Inside Out (2015).

The only Pixar film directed by Pete Docter not produced by Jonas Rivera.

Pete's Barber Shop is named for director Pete Docter.

The fancy restaurant that Mike takes Celia to, Harryhausen's, is reference to 'Ray Harryhausen' *qv) one of the earliest practitioners of stop-motion photography and claymation. Harryhausen is responsible for bringing a number of now-iconic monsters to life in films such as Jason and the Argonauts (1963), The 7th Voyage of Sinbad (1958)., and Clash of the Titans (1981).

Pete Docter's only film to not have any characters voiced by Pixar's Josh Cooley, since he hadn't joined Pixar at the time.

Sulley and Boo's relationship is possibly based on Baloo and Mowgli in The Jungle Book (1967) and just like how Mowgli runs away from Baloo because he is forced to go to a man village Boo avoids Sulley after he accidentally scares her when doing a mock roar for Mr. Waternoose. Sulley is also similar to Baloo in appearance as he looks like a bear except he has horns and a long tail and is about the same height and bulk as Baloo. Plus 'John Goodman' voiced Baloo in The Jungle Book 2 (2003) and in that film Baloo scares a older girl named Shanti much like Sully scared Boo who is a younger girl.

Patrick Stewart was considered for the voice of Waternoose.

On the scare floor leader board, the name immediately below Sullivan and Randall is Ranft, a reference to longtime Pixar writer Joe Ranft.

The reason for the hidden base in the factory is because the film makers feared that it may become claustrophobic for viewers , seeing the same halls and locker rooms over and over again.

The J is backwards on the border in the test room.

A113 can be seen listed on the walls of where the doors go to, simply as "A13".

Pete Doctor's only Pixar film to be released on Vhs, Up (2009) and Inside Out (2015) were both released only to DVD.

This is the only Disney/Pixar film not to have a paperboard slipcover with its DVD/VHS release.

One of the 3 Pixar Films where Joe Ranft voices someone to have Ranft simply listed in the Additional Credits. The other 2 films being Toy Story (1995) and The Incredibles (2004).

The abstract "Mumbo" poster on the wall in Sulley's bedroom mimics the style of 1950s artist and album-cover illustrator Jimmy Flora.

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.

The name of the sushi restaurant where Mike is on his date is called "Harryhausen's." This is a direct nod to famed pioneer in stop-motion animation Ray Harryhausen, who worked on famed films like King Kong (1933) and Jason and the Argonauts (1963).

This film remains the only Pixar film where Daniel Gerson voices a character, being Smitty and Needleman, with him having passed away in 2016, though his last film worked on 16 years later being Cars 3 (2017) is dedicated to him. The only other film where he voiced a character is Big Hero 6 (2014), which is not by Pixar.

Pixar's only film where the logos are shortened at the start of the film, where they appear as seen in trailers (and outros to films in the case of the Disney Logo), pretty much to help accompany the music that plays during the title screen, but they do appear as normal after the credits.

The movie Little Monsters (1989) starring Fred Savage and 'Howie Mandel' was the inspiration for this film.

John Goodman and Billy Crystal who voiced Mike and Sulley previously starred in The Adventures of Rocky & Bullwinkle (2000) respectively as an Oklahoma cop and a mattress salesman.

Steve Buscemi voiced two revolutionary CGI films in one year - Final Fantasy: The Spirits Within (2001) (first photorealistic CGI film) and Monsters, Inc. (2001) (photorealistic fur)

The controls for the Monsters Inc. door mechanisms include a button that starts the process labeled "FIZT". At the time, Fiz-T (Physics-Tool) was 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. Another button, "IKT," was the name of Pixar's "Inverse Kinematics Tool."

At the start of the film Mr. Bile during the scare simulation scene causes comedy mayhem by suffering amusing injuries. This foreshadows the end of the film where instead of scaring kids the monsters instead make them laugh as it is apparently more powerful than scaring.

According to the original character design sketches found on the DVD, Fungus's first name is Jeff and his surname was originally "Frungus".

Baby Smitty is voiced by Joe Ranft's daughter, Sophia Ranft.

2319 in addition to W and S being the 23rd and 19th letters of the Alphabet respectively may also refer to the year that The Disney Company was founded- 1923.

The monster in the opening scene doing the scare test is asked to confirm his name is "Mr. Bile" to which he replies that his friends call him "Phlegm", referencing that bile in the human body is commonly/casually referred to as phlegm.

When animating Sully's fur in situations where he would run, it proved to be a difficult task. You can see the tests on the DVD.

Though not her real name Boo is named that by Sulley due to her constantly saying 'Boo!'.

Currently Pete Docter's only film to have a follow up film. Up (2009) and Inside Out (2015) are still yet to have one.

If you Google "2319," you'll find that Chapter 18, Section 2319 of the U.S. Code pertains to criminal infringement of a copyright.

The first Pixar film of the 2000s.

Running gags in the film include Mike being happy his face is in mass media despite his face being covered on TV and a magazine respectively, the CDA being informed of 2319 with George being the main victim, Boo causing panic among the monsters due to her being 'toxic' and Mike and Sulley attempting to return Boo back to her room but fail.

Dan Aykroyd, George Wendt and Steve Martin were considered for the role of James P. Sullivan.

Eddie Murphy, David Schwimmer, Drew Carey and Sinbad considered for the role of Mike Wazowski.

Ian McKellen, Brian Blessed, Leonard Nimoy, Alan Rickman and Christopher Lee were considered for the role of Waternoose.

Chris Barrie, Jeff Goldblum and Vincent D'Onofrio were considered for the role of Randall Boggs.

This is the first Pixar feature to have the "Created and Produced at Pixar Animation Studios, Emeryville, California" credit at the end.

The movie takes place in the summer of 1999. This is confirmed earlier in the movie when the camera focuses on one child's scare record. His scare dates take place between February 1999-June 1999, so it's safe to say that the next scare will take place in June or July.

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.

The sequence where Sully thinks that Boo has gone through the trash compactor is an almost shot-for-shot remake (and an homage to) the Warner Bros Looney Tunes cartoon short Feed the Kitty (1952). In that cartoon a bulldog named Marc Antony mistakenly believes that Pussyfoot, a kitten he has adopted, has been made into a cookie.

When Sulley is about to say goodbye to Boo, Boo is trying to get him to play. A doll of Nemo appears. This is the first appearance of the character who would be the focus of Finding Nemo (2003), storyboarded before this movie but not completed until two years later (Marlin also appeared here in a portrait behind the Harryhausen chef and Nemo decorated the wall of a room Randall was thrown into). Boo also hands Sulley a Jessie the Yodeling Cowgirl doll, which first appeared in Toy Story 2 (1999) and the Pixar ball originally from Luxo Jr. (1986).

In the ending sequence when the monsters make children laugh instead of scream, 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.

Randall Boggs is last seen in the trailer home from A Bug's Life (1998), next to the Pizza Planet truck from Toy Story (1995). The man inside the trailer is the same model as the simulated boy from the first scene. The mom is the same boy but with a "bun" placed on his head.

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).

Whenever the CDA Arrives, Roz tends to pull down the shutter to her office, likely to hide the fact that she's the leader.

The company play at the end of the film features Mike singing "she's out of our hair" whilst sitting on a stool this is a parody of the 1980 song and video to "She's out of my life" by Michael Jackson.

The music when Sulley leaves Boo is the same music in Toy Story 3 (2010) when Andy leaves Woody and crew.

The signal for the CDA, 2319, may be a reference to the letters "W" and "S", which are the 23rd and 19th letters of the Latin alphabet. WS may stand for "white sock", a common threat to monsters, which can only be ridden by the CDA. W and S are also the initials of Mike and Sulley's last names (Wazowski and Sullivan).

During the film's chase sequence, one of the places Mike, Sullie, Boo and Randall end up in on Earth is Paris, which would later be the setting of one of Pixar's later films, being Ratatouille (2007).