Monsters Inc. is the movie that so many adults today grew up watching as kids. This November will officially mark twenty years since the animated monster movie was released in theaters. Along with Disney and Pixar’s other movies, Monsters Inc.’s story and characters had a huge influence on a lot of people’s childhoods. Mike, Sulley, and the other monsters in Monstropolis are characters that kids have been able to look up to for years and still look up to today.

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This amazing and iconic movie didn’t come easy though. It took the filmmakers a lot of hours and hard work to make everything in the movie look believable, but magical at the same time. Here are 10 fascinating behind-the-scenes facts about the Pixar film.

10 A Pixar Story Artist’s Daughter Voiced Boo

The filmmakers originally tried voicing Boo themselves, but it didn’t make sense with an adult’s voice, so they had to find a kid to play her. Luckily, Rob Gibbs, one of the story artists working on the movie, had a little girl that was around Boo’s age. Since she was so young at that time, the filmmakers had to get creative to record her. Mary Gibbs, who plays Boo, said, “They would follow me around the recording studio, use puppets to talk to me, and have my mom tickle me or take money/candy away from me to make me laugh and cry… all real emotions.”

9 Mary Gibbs Had To Make Up The Lyrics To The Song Boo Sang In The Bathroom

When the filmmakers were recording Mary, they asked her to sing a song for the scene where Boo is singing in the bathroom. But it had to be a song of her own. Mary Gibbs told Reddit, “They told me to sing and I started singing 'Wheels on the Bus,' but they couldn’t use any actual songs [because of] copyright issues so they had me babble and sing random words for a few hours and took out the parts they liked the best!”

8 'Monsters Inc.' Was The First Animated Movie With CGI Fur

Have you ever wondered how Sulley’s fur looks so realistic? Pixar developed its own software program called Fizt, which was able to simulate all of his fur as he moved so the animators wouldn’t have to animate each individual hair. “Sulley has 2,320,413 unique hairs on his body,” according to Oh My Disney. It took 12 hours to animate one frame when they first tried to animate each hair, so they did something no one did before and changed 3D animation forever.

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7 Almost Every Monster Was Created With The Same Tongue

Each monster in the film is unique, but a lot of them have one thing in common—they have the same tongue. According to Oh My Disney, “90% of all the monsters in the film have Mike’s tongue.” Each character has to be modeled on the computer (which is pretty much the CGI version of sculpting), so maybe the filmmakers wanted to make it easier to create them.

6 Billy Crystal And John Goodman Recorded Their Lines Together

Billy Crystal is the hilarious comedian responsible for Mike Wazowski’s voice and goofy personality. But that funny personality didn’t truly come out until he worked side by side with John Goodman who voices Mike’s best friend, James P. “Sulley” Sullivan. Billy Crystal told Dark Horizons, “I did the first two sessions alone and I didn’t like it. It was lonely and it was frustrating." John Goodman also commented on the experience and told BBC, “When Billy and I got together, the energy just went through the roof, so it was great." Most of the time actors record their lines separately when they’re voicing animated characters, but the decision to put Billy and John in the same room made the movie one that so many people love.

5 A Muppeteer Voiced Randall’s Assistant, Jeff Fungus

Director Pete Docter is a “huge Muppet fan,” so he had to work with a muppeteer for the movie. The legendary muppeteer, Frank Oz, voiced Randall’s assistant, Jeff Fungus, who Randall just calls “Fungus” and bosses him around to help him with his evil plan. He’s voiced a lot of other characters too. “Yoda, Miss Piggy, Fozzie Bear, and Cookie Monster are just four of the most famous, and incredibly distinct, characters that the legendary Frank Oz voices,” according to Mental Floss. He also voiced Subconscious Guard Dave in Inside Out.

4 The Sushi Restaurant’s Name Has A Special Meaning

One of the plot twists in the movie is when Boo escapes Sulley’s bag in the sushi restaurant where Mike was trying to have a romantic date with Celia and she scares all of the monsters in there. Since it’s such an iconic scene, the filmmakers carefully selected the name of the restaurant and named it after a legendary artist. According to Oh My Disney, “Harryhausen’s is named for Ray Harryhausen, a pioneer of stop-motion animation.”

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3 The Door Vault Has Millions Of Doors In It

Another iconic scene in the movie is when Mike and Sulley are trying to keep Boo from Randall and end up in the door vault. It’s one of the most complex scenes Pixar has ever done, but the result was amazing. The team at Pixar created millions of doors to make it look like a real Door Vault where you could go to different parts of the world with each door. According to Oh My Disney, “There are about 5.7 million doors in the Door Vault.” That’s definitely a lot of work, but it’s so magical to see it come to life in the movie.

2 The Movie Almost Had An Entirely Different Story

Pete Docter told Jeff Goldsmith on his Creative Writing podcast, “My idea was that what it was about was a 30-year-old man who is like an accountant or something, he hates his job, and one day he gets a book with some drawings in it that he did when he was a kid from his mom. He doesn’t think anything of it and he puts it on the shelf and that night, monsters show up. And nobody else can see them. He thinks he’s starting to go crazy, they follow him to his job, and on his dates… and it turns out these monsters are fears that he never dealt with as a kid… And each one of them represents a different kind of fear. As he conquers those fears, the guys who he slowly becomes kind of friends with, they disappear… It’s this bittersweet kind of ending where they go away, and so not much of that stayed.” Nothing can ever replace Monsters Inc., but maybe one day this could turn into a different movie.

1 Parenthood Changed Pete Docter’s Perspective On The Movie

Pete Docter and the other filmmakers had a hard time finding what Monsters Inc. was really about in the beginning. When they showed other people material from the movie, they didn’t really understand it. But when Pete Docter had a child, he finally realized what it should be about. At the Los Angeles Film Festival, Pete Doctor said that having a child “changed everything” and he explained that the film eventually became more about Mike and Sulley’s "struggle between the love of family and the love of work.”

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