Sundance has seen its share of both rapturous and disastrous movie premieres, but few big openings in recent memory have produced the sort of hyper-polarized — and downright guttural — reactions that Swiss Army Man elicited this past January.

“We expected laughing and cheering, but I think I heard some people literally just screaming, a very animalistic screaming,” Daniel Kwan, the film’s co-director, told Inverse in a recent conversation in New York. “A couple piercing shrieks, that were neither joy nor disgust, but something in between.”

And that was just in the first ten minutes.

To be fair, no one knew much about the film, which Kwan co-wrote and directed with creative partner Daniel Scheinert (together, they are known as The Daniels). There was a curious still photo from the film in the festival guide, and a cast list — with Paul Dano, Daniel Radcliffe, and Mary Elizabeth Winstead — good enough to earn it the burden of hype from journalists and buyers. The information blackout — if not the expectations that filled in the blank spaces — was very much by design.

“The fun thing about [the premiere] was that we didn’t tell anyone what the movie was about, on purpose, so we could get that moment, to see what the spectrum of reactions would be,” Kwan said. “That was kind of the fun, existential joke of it all. We wanted to create something that just did not belong anywhere, especially not Sundance.”

And a movie about a suicidal man, his farting corpse best friend, and the fantasy land they inhabit definitely fit the bill, even at a festival known for ushering in eras of indie film innovation.

The first shrieks likely came when Radcliffe, playing the weatherbeaten corpse that washes ashore on a deserted tropical island, lets out a prolonged, bubbly fart. It surprises the sad and desperate Hank (Dano), who had hoped against hope that the body was a living person who might rescue him. The farts, however, turn out to be more than the wheezing biological accordion of dead organs pushing stale air from a lifeless body; instead, Manny — as Hank names the corpse — awakens, and uses an endless stream of powerful anal emissions to skim across the water like a jet ski. And Hank, figuring he has no better shot at escape, rides him like a Sea-Doo.

Thus begins the semi-absurdist romp that makes up the film’s entire second act, and regardless of how much the film’s subtext or surprisingly emotional character arcs connect with an audience member, the visual flair and inventiveness on display throughout Kwan and Scheinert’s debut feature is undeniable.

Given both their predilection for creating unlikely, gravity-defying images in their careers as music video directors (like the clothing guns in this Joywave video), and the very small budget with which they had to work (“the movie is so weird that we didnt take it personally when financiers said no,” Scheinert admitted), the obvious choice was to shoot as many of the wild stunts and optically confounding scenes on set, rather than through CGI.

And that’s exactly how they approached the film’s first big stunt, the scene in which Dano rides Radcliffe’s rigid corpse across the ocean.

“Our usual plan for visual effects is to shoot practical things and then remove wires,” Scheinert said. “The opening sequence is real people getting dragged across the ocean, and we just had to remove stuff. Sometimes we removed the boogie board that you could see he was riding on, or some cables or boats in the distance. Sometimes it was a stunt man on a dummy, there was one take of the whole scene with actual Paul riding actual Daniel.”

As you might expect, both actors embraced the adventure.

“It was glorious; they were so happy,” Scheinert said. “As opposed to having to act on a green screen, they were slamming into waves; Paul was singing at the top of his lungs in the actual ocean. That was how we kind of got them to sign up. They read the opening of the movie and said, ‘That sounds awesome,’ and we told them we were really going to do it.”

As Manny begins to awaken, his limbs become more nimble and his joints, though still creaky, regain some range of motion. The expanded physicality provides Hank with many other uses for his swiss army man. He provides Hank with fresh drinking water through an endless fountain flowing forth from his mouth —shot through an “Exorcist-type rig,” Scheinert said, designed after a model was made of Raddcliffe’s jaw — and then learns to fire acorns like bullets from his mouth, chop wood with his arm like an axe, and fly up through the air as if some sort of high-jumping dolphin.

That last stunt required some CGI, because they shot it in a pool against a green screen instead of submerging stars in the water, but beyond that, Radcliffe was game to do the rest.

“He was pretty adamant about being in almost every scene,” Kwan said. “He wanted to give Paul something real to act off of. So we built these dummies just in case our Harry Potter A-list actor decided he didnt want to lie in the dirt for a couple hours, but he did it. It adds to the impossibility of it. The first 20 minutes of the film we were just hoping the audience would sit there just wanting him to come alive and also wondering, why did he do this movie?”

For The Daniels, signing up Radcliffe was a no-brainer, given both his star-power and willingness to try new things. Then they learned he had immense control over his body — and looked the part.

“His skin is already the color of a dead person,” Scheinert laughed. “He has the whitest skin, you can already see veins, so all we had to do was augment them.”

Both the makeup work and extreme length to which they stretched Radcliffe’s body made for some surprised — and, at times, animalistic viewers, but that was all by design.

“Hopefully it’s a rewarding thing where we push them to the point where they themselves are surprised by it,” Kwan said. “Like, ‘Oh, OK, I thought this was going to be unbearable, but actually something odd is happening in my heart right now.’”