It’s nearly impossible for one to think of the movie Up and not feel his or her heart explode. The memory of the film’s unforgettable opening sequence alone is enough to bring a stray tear to even the most hardened moviegoer’s eye. That’s how powerful the Oscar-winning animated film still is. Directed by Pete Docter and Bob Peterson, Up tells the story of a bitter, widowed old man who escapes into solitude (by attaching millions of balloons to his house) to the mythical Paradise Falls, only to find Russell, a stowaway scout who has hitched a ride and changes the course of his life entirely. Here are 15 things you might not have known about Up.

1. THE BEGINNING MONTAGE ORIGINALLY HAD CARL AND ELLIE COMPLETING EACH OTHER’S SENTENCES.

According to co-director Peter Docter, the famously heart-wrenching sequence, titled “Married Life,” which traces Carl and Ellie’s life together, was originally supposed to have dialogue. “Bob Peterson originally wrote a series of very short scenes, two or three on a page with dialogue, and the characters were completing each other’s sentences and other snippets that showed how well matched they were,” Docter told the Los Angeles Times. “And as we went into storyboard, Ronnie Del Carmen, who was our head of story, took on that sequence at the beginning and said, ‘This would be really great if it was silent.’” Admittedly, Docter and his colleagues initially resisted the suggestion. “We even had sound effects in that sequence for a long time, like the jars with their money to South America smashing and the tire in the car popping,” the director continued. Eventually, though, they relented. “We took all that stuff out as well and left just Michael Giacchino’s score.”

2. THE BEGINNING MONTAGE WAS INSPIRED BY A BUNCH OF STRANGERS’ HOME MOVIES.

While some of the moments in Carl and Ellie’s life were pulled from the filmmakers’ own lives, they also did some research into the lives of other people. “Strangely, we got a couple of home movies from the Internet—Michael Giacchino has a collection that I think he ordered from eBay,” Docter told the Los Angeles Times. “We had no idea who the people in them were, but we’d watch their lives progress and piece them together—we’d note, ‘Oh, now there’s a new kid in the picture. And what happened to that person? I guess they must’ve moved away.’ It was strangely compelling.”

3. THE ROOM NUMBER A113 IS SEEN OVER CARL WHEN HE’S SUMMONED TO COURT.

A113 is one of Pixar’s most prevalent Easter eggs, having appeared in Toy Story, Monsters, Inc., Ratatouille, WALL*E, A Bug’s Life, and Inside Out, among others. “A1-13 was the animation classroom at California Institute of the Arts in the Character Animation Program,” John Lasseter, chief creative officer at Pixar and Walt Disney Animation Studios said in a YouTube interview. “CalArts is one of the best animation schools … and a lot of the students … as they created films—short films and feature films—they’ve kind of hidden A113 in the movies.”

4. PETE DOCTER IMAGINED CHARLES MUNTZ AS CARL’S DARK SIDE.

Essentially, the film’s antagonist is Carl’s most extreme version of himself. “Muntz is kind of where Carl would have gone had he been allowed to take it to the end of the line,” Docter told Screen Crave. “He’s just so obsessed and in a sense in Carl because that part of him dies away. Muntz is a sort of symbol of that ... So Carl is left with letting go of the stuff and his old idea of what adventure is as personified by Muntz and instead embraces the present and connects with Russell.”

5. DOCTER AND HIS ANIMATION TEAM INTENTIONALLY DREW CARL SQUARE AND RUSSELL ROUND.

To the filmmakers, the characters’ shapes were representative of their personalities. “[Square] just felt like a good way to represent the way Carl was inside—he’s a boxed-off, by-the-book, self-enclosed guy,” Docter noted in an interview with Movie Retriever. “He lives in a house that’s a square. A lot of the shots we tried to compose had Carl framed in squares. Contrasting that, you have Ellie, who is more of a circle and full of life. The two of them work out well together but once she’s gone, Carl is stuck in this little box. Russell we tried to make more like a balloon shape with an upward direction that makes him more full of energy and buoyant and bouncy and so on. It seemed to contrast Carl well.”

6. THE STATION AGENT INSPIRED UP. 

YouTube

Who would’ve thought a Peter Dinklage-led indie movie would’ve inspired one of Pixar’s most celebrated films? “We looked at how other people have dealt with the subject matter,” Docter told Movie Retriever. We looked at The Station Agent, a great, simple, character-based story of a guy who’s much like Carl, who comes out of his shell. Casablanca is a similar kind of story ... Movies that had a beautiful simplicity to them and a focus on character.”

7. A BOY NAMED RUSSELL JANG WAS THE INSPIRATION FOR RUSSELL IN UP.

Growing up in Piedmont, California, Jang lived next door to Pete Docter. “I was really energetic and sporadic,” now-college student Jang recalled to the Gonzaga Bulletin. “I would go over a lot and usually just walk right in. The way I figure, if they left it unlocked, then I was fine to go right in.” According to Jang, he found out about his part in the film over dinner with the director one evening while he was in grade school.

8. OSCAR-WINNING COMPOSER MICHAEL GIACCHINO WROTE THE SCORE BY EXPLORING WHAT KINDS OF MUSIC REFLECTED CARL’S GENERATION.

If you ever wondered why the score sounds so old-timey, it’s because it is. “I kept thinking about ... what styles of music [Carl] must have lived through in [his] 78 years, starting back to the very early ’30s which was still pulling from the ’20s, moving into some swing stuff, moving into big, bold adventure music,” recalled Giacchino in an interview. “For me, I kept drawing on what things he enjoyed growing up.” In the feature Composing for Characters, Docter recalled his addition to the score, “I remember saying ‘keep it really simple ... imagine it playing on a music box.” Hence, the final tune you hear in the film.

9. WALT DISNEY INSPIRED THE CHARACTER OF CHARLES MUNTZ.

As did classic actors Spencer Tracy, Walter Matthau, and James Whitmore. “For Muntz we modeled him on strong, 1930s-era adventurous types,” Docter mentioned in a roundtable interview with Big Shiny Robot. “Errol Flynn and Walt Disney were two inspirations, as well as real life adventurers like Roald Amundsen and Percy Fawcett.”

10. DOCTER AND PETERSON CHOSE TO SET THE ADVENTURE IN SOUTH AMERICA TO REFLECT CARL’S EMOTIONAL STATE.

Just as Carl’s house is as much a character in the film as the actual characters, so is the film’s climax locale. “The Tepuis, or tabletop mountains, of South America are old, isolated, rugged, dangerous but with a soulful beauty—a pretty good description of Carl,” Peterson told Big Shiny Robot. Additionally, the film crew took a trip to South America as they cobbled together the script. He added, “Going there gave us a good sense of what it would be like for Carl and his friends to be up there. In the film, we used a great many plants and rock shapes that we saw from the Tepui.”

11. THE DIRECTOR’S DAUGHTER VOICES, AND IS THE INSPIRATION BEHIND, ELLIE.

“My daughter did the voice of young Ellie in Up—that spirited, spunky kid with hair out to there—and she was a lot like the character at the time,” Docter said, according to Midday. It’s no secret that that same little girl would go on to be the driving force behind Docter’s next film, Inside Out.

12. JORDAN NAGAI, WHO VOICED RUSSELL, WOULD RUN AROUND BEFORE SAYING HIS LINES TO CAPTURE HIS CHARACTER’S RESTLESS SPIRIT.

In an interview with the Los Angeles Times, Docter recalled the ways he’d get his young voice actor into character. “We would come up with games,” Docter noted, with Nagai beside him. “I would say, ‘Jordan, next time before [you say the line], run over there, run around the chair three times, jump up and down three times,’ and you would do it. A lot of times that would make you more energetic.” At one point, then-nine-year-old Nagai, who was chosen from over 500 kids who auditioned, was even picked up and tickled upside-down by the director for a line where he had to laugh.

13. PETE DOCTER AND OTHER CREW MEMBERS POSED AS MUSICIANS AT AN OLD FOLKS HOME TO RESEARCH UP.

More than simply drawing from their experiences with their own grandparents, the filmmakers observed other elderly people to help them pull off Carl’s grouchy old man. “We went to an old folks’ home, a group of us, we went posing as musicians. We had a little band ... we played jazz tunes,” Docter told DP/30. "I played bass and at the same time we were spying at all the old folks who were watching us.”

14. THE FINAL BALLOON COUNT WAS 10,297.

You can stop counting now: the film’s FX technical directors Jon Reisch and Eric Froemling have done the work for you. “The entire canopy is filled with balloons,” Reisch recalled to Tech Radar. “We didn’t just simulate the outer shell.” Yep, beneath the outer layer of balloons you see tugging the house are several more layers, each as carefully animated as the first.

15. PETE DOCTER AND BOB PETERSON WATCHED ED ASNER IN A PLAY ABOUT A HOLOCAUST SURVIVOR WHEN THEY WERE CONSIDERING HIM FOR CARL.

Yeah, even Ed Asner was wondering how he got the part with such a bleak intro to his work. “I have a good voiceover agent who submitted me along with a few of his other clients. Fortunately, Pete Docter and Bob Peterson were aware of my work and they came to watch me in a one-man reading I gave in San Francisco where I was playing the part of a Holocaust survivor,” Asner told The Wall Street Journal. “How they thought a Holocaust survivor would blend in with the concept of Up, I’m not sure.”

According to Docter, however, the moment he knew he would cast Asner was much more lighthearted. “The first time Ed saw the model we’d made up of Carl here at Pixar, he looked at it and gruffly said, ‘That doesn’t look anything like me,’” Docter recalled to DP/30, imitating the veteran actor. “That’s when I knew he was perfect for the part.”