When Daniel Radcliffe left the “Harry Potter” franchise behind, it was clear he intended to do more than merely coast on his wizardly glory. He appeared nude on stage in “Equus.” In films, he’s played Allen Ginsburg, Igor, and a guy who sports devil horns. He’s demonstrated his appreciation of the works of Tom Lehrer. In other words, he’s not playing it safe.

But his role as a farting corpse in “Swiss Army Man” is the most outrageous thing he’s done yet. It also might be the best. Yes, you read that right. Daniel Radcliffe plays a farting corpse. He’s discovered one day, having washed up on a beach, by a castaway named Hank (Paul Dano) who has just failed an attempted suicide by hanging. (Have I mentioned this is a comedy?)

Daniel Radcliffe and Paul Dano star in “Swiss Army Man.”

Intrigued by the lifeless body he eventually dubs “Manny,” Hank discovers that its flatulent emissions are powerful and long-lasting enough to serve as propulsion, and before you can say “Weekend and Bernie’s,” Dano is riding Radcliffe like some fleshy Jet-Ski on a quest to get back home. If that’s enough to make you cross this one off your must-see list, fair enough. But these opening salvos of absurdist, body-function humor are almost a test, and if you get on the movie’s wavelength, it yields surprising rewards.

For one thing, there’s Radcliffe’s performance. It might be a minor spoiler to reveal that Manny eventually gains at least a semblance of mobility, but you don’t cast a big star in your movie just to have him lie there, even if you’re as willfully perverse as directors Dan Kwan and Daniel Scheinert (billed collectively as “Daniels”). And as he evolves from flaccid-limbed passivity to…something else…Radcliffe demonstrates a remarkable level of physical control, creating emotional resonance and personality, as well as slapstick guffaws, before ever using words.

True to the title, Manny helps Hank survive in the wilderness in many ways, acting as canteen, compass, and axe. He also helps Hank come to terms with memories involving a mysterious girl, Sarah (Mary Elizabeth Winstead). Sometimes you just need someone to talk to. Other times you need a dead man to dress up like the obscure object of your desire and act out interactions on a bus constructed from trash people have thrown in the forest. It’s complicated.

The only real hiccups in “Swiss Army Man” come towards the final act, where the desire to make sense out of all this insanity somewhat tarnishes the scatological bromance brilliance of the first hour of the film. This is the first feature by Daniels, following several bizarre and visually inventive music videos (“Turn Down for What”) and shorts.

In one of the latter, 2014’s amazing “Interesting Ball,” a character says “If the universe is as infinite as they say it is, then these weird things that are happening aren’t just possible, they are inevitable.” That may be freshman-dorm-level cosmology, but it’s also true, and it certainly helps explain the worldview of two young filmmakers with imagination to burn.

(Have I mentioned this also, sort of, a musical?)

(“Swiss Army Man” opens Thursday, June 30, at the Hollywood Theatre and other locations.) GRADE: B+