Reporting by Josh Horowitz

Butt doubles are common in Hollywood. After all, some actors do like to maintain an air of mystery. But Daniel Radcliffe is not one of those people. Trust me, you see plenty of his butt in his wacky and delightful film "Swiss Army Man." The film is like a celebration of Radcliffe's (hairy) butt cleavage -- and it's glorious.

However, that doesn't mean there isn't a prosthetic mold of DanRad's butt in a dusty production closet somewhere. According to Radcliffe, directors Daniel Kwan and Daniel Scheinert asked for a mold of his butt to pull off their ambitious opening sequence, which famously sees Paul Dano riding Radcliffe across the ocean like a jet ski, propelled solely by the power of the former's farts.

"It was not dignified," Radcliffe told MTV News at the Sundance Film Festival Saturday (Jan. 23) night of the butt-molding process. "But it was like, 'It's gonna be a great movie. It's gonna be a great movie.'"

Meanwhile, the film's excessive flatulence was authentically captured using real farts from the cast and crew. "Everybody on the crew was invited to record their own," Dano said, before Radcliffe explained how during one particular take, Dano felt some gas coming on, so he grabbed the boom mic and, uh, let it rip. Right there. On set. In front of everyone.

Of course, it was up to the directors to decide which farts would make the final cut. "Real farts are in there," Dano said. "But I'm not sure if any are ours."

Now, that's what I call movie magic.