For Pixar’s fourth award-winning feature, director Pete Docter and crew delved into the monster realm. The perfect family flick—one that both plays for children but winks at the adults who bought the tickets—Monsters, Inc. tells the story of BFFs Mike Wazowski (Billy Crystal) and James P. “Sulley” Sullivan (John Goodman), a couple of scarers at the titular Monsters, Inc. who generate the city’s power by scaring little kids, even though they themselves are afraid of children.

However, when one little girl named Boo sneaks into their city of Monstropolis, the duo must face their fears and race to return her to her world. Before you pop that Blu-ray back in and cozy up with the kids, learn more about this technologically groundbreaking film with these 10 fun facts.

1. BILL MURRAY WAS THE FIRST CHOICE TO VOICE SULLEY.

According to Robert Schnakenberg’s The Big Bad Book of Bill Murray, the beloved actor tested for the role of Sulley. However, when producers tried to offer him the part, he couldn’t be reached. Thus, they took his silence as a “No.” 

2. STORY ARTIST ROB GIBBS’ TWO-YEAR-OLD DAUGHTER INSPIRED BOO’S CHARACTER.

In an interview with Dark Horizons, executive producer John Lasseter described the process of finding Boo’s voice. “We initially started doing the voices ourselves for Boo, and it just popped you out of the film to have an adult voice. So, one of the story guys, Rob Gibbs, had a two-and-a-half-year-old daughter [Mary] and we brought her in and initially we were going to record her just doing the lines,” explained Lasseter. “I’d say, ‘Okay, now pretend you’re really scared.’ And she would just go and run away and play and it was just really hard to get her to stand there ... We got her to say kitty and a couple of other things, but the rest of all the vocalizations were just real noises that she made.” However, since production took about five years, Mary Gibbs eventually started developing her speech. Thus, Lasseter and crew had to take another approach. He continued, “As she got older, she started speaking English to the point where the editors would go back and turn it back into nonsense.”

3. BOO’S REAL NAME IS MARY.

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You’ll notice the small detail repeatedly signed across some of Boo’s drawings in the film. In a Reddit AMA, Mary Gibbs recalled the process of getting into character during recording sessions: “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.”

4. FOR THE SONG BOO SINGS ON THE POTTY, PRODUCERS HAD HER MAKE UP HER OWN LYRICS.

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In her Reddit AMA, Mary Gibbs recalled the process of putting the tune together. She noted, “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!” 

5. PETE DOCTER’S ORIGINAL PITCH WAS TO HAVE A GROWN MAN BE HAUNTED BY THE MONSTERS HE DREW AS A KID.

On Jeff Goldsmith’s Creative Writing podcast, director Pete Docter recounted his original pitch: “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.” 

6. THE FILM WAS THE FIRST TO INTRODUCE THE ONSCREEN REPRESENTATION OF FUR.

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In order to animate each individual strand of hair on Sulley, which reportedly took 12 hours to fill a single frame, Pixar developed a new software program called Fizt. According to WIRED, the software was extremely advanced for its time, as it had the power to simulate each of the three million hairs that covered the lovable monster. “We made the simulator able to digest anything,” said Andy Witkin, one of the studio’s senior animation scientists. 

7. JOHN GOODMAN AND BILLY CRYSTAL RECORDED THEIR LINES TOGETHER—A RARITY IN ANIMATION.

Typically, voice actors get into the booth at separate times to record their dialogue. But Billy Crystal pushed for the opportunity to work alongside his co-star, John Goodman. “I did the first two sessions alone and I didn’t like it," Crystal told Dark Horizons. "It was lonely and it was frustrating." Goodman was also a fan of the joint process; he told the BBC: “When Billy and I got together, the energy just went through the roof, so it was great."

8. RANDY NEWMAN WON HIS FIRST OSCAR FOR HIS ORIGINAL SONG, "IF I DIDN’T HAVE YOU."

It was Randy Newman's first Oscar win out of 16 nominations. In 2011, he won his second Oscar for "We Belong Together" from Toy Story 3, another Pixar project. To date, Newman has earned 20 Academy Award nominations.

9. MUPPETEER FRANK OZ VOICES RANDALL’S ASSISTANT, JEFF FUNGUS.

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. Casting Oz was truly a dream come true for Pete Docter, who is a self-proclaimed “huge Muppet fan.” Docter reunited with Oz, along with another force behind The Muppets, Dave Goelz (a.k.a. Gonzo), for Inside Out.

10. HAVING A CHILD HELPED DOCTER UNDERSTAND THE HEART OF MONSTERS, INC.

When Docter was first piecing the film together, he simply couldn’t get to the heart of the story. “When the film started to come together people were bored by it,” Docter said during a Q&A at the Los Angeles Film Festival. “They didn’t really understand what the film was about. ‘What do you mean,’ I said, ‘It’s about monsters!’”

At the time, Docter and his wife had just had their first child, which forced him to find a balance between work and home life. And that was what made the theme of the film ultimately click. "It changed everything for me," Docter said of fatherhood. "I had been working in, and loved animation. I couldn’t wait to get to work. I’d spend hours and hours there. And now I had a kid, and my wife would call and be like, ‘He smiled for the first time.’ And I would be like, ‘Grgh! I’m at work, but I want to be at home!’” So for Docter, the film became more about Sulley and Mike's "struggle between the love of family and the love of work.”