Yes, there’s poop, pee and masturbation in the very weird ‘Sasquatch Sunset,’ but it’s also a surprisingly moving film

Starring Riley Keough, Jesse Eisenberg, Christophe Zajac-Denek and Nathan Zellner. Written by David Zellner. Directed by David and Nathan Zellner. Opens Friday at TIFF Lightbox. 89 minutes. STC

David and Nathan Zellner’s “Sasquatch Sunset” was the weirdest and most divisive offering at this year’s Sundance Film Festival, prompting both cheers and walkouts for its gross-out depictions of Bigfoot daily life.

In fact, it might be the most head-scratching and audience-baiting film ever to screen at Sundance. That’s really saying something about a fest that champions unique indie cinema and that once premiered “A Ghost Story,” David Lowery’s nearly wordless phantasmal drama in which Casey Affleck mopes about beneath a bedsheet.

The Zellner Bros. love to challenge audiences. Their oater “Damsel” upended cowboy code and their dramedy “Kumiko, the Treasure Hunter” took the Coen Bros. crime fiction “Fargo” literally. But “Sasquatch Sunset” is outré even by the Zellners’ wacky standards. It’s also a surprisingly moving tale, in its own big, dumb furry way.

It answers a question no one ever thought to ask: What if the man-apes in the “Dawn of Man” sequence in “2001: A Space Odyssey” didn’t have a visiting alien monolith to teach them how to use bones to club food sources and each other?

“Sasquatch Sunset” suggests the man-apes would have ended up much like the four hapless hairy hominids we meet somewhere in the forests of Northern California, during a full year of gawking.

It’s an area known for Bigfoot sightings, including the one famously seen in the 1967 Patterson-Gimlin film that has long been hailed or debunked, depending on your willingness to believe — or not. The Zellners modelled their Bigfoots (Bigfeet?) on the one glimpsed in that celluloid fragment; they also delved into online cryptid discussions.

The lush forest where the Sasquatches reside is a beautiful wild place, one that cinematographer Mike Gioulakis (“It Follows”) lenses with devotional awe, like a feral David Attenborough.

The Zellners’ hominids are one harassed female and three annoying males, played by a well-disguised Riley Keough, Jesse Eisenberg, Christophe Zajac-Denek and the very busy Nathan Zellner, who besides co-directing the film also co-stars in it. The complete investment of the actors into these creatures is something to behold, especially considering how uncomfortable the costumes were, by their own accounts.

The movie is wordless, unless you count the many “ohs,” “huhs” and “aarghs!” uttered by the Sasquatches. They look and sound like a biological orchestra tuning up as they stooge around emitting all manner of noises and effluence, while engaging in masturbation, non-consensual sex (evidently), skunk-sniffing, snake-petting and mountain-lion baiting.

They seem oblivious to the dangers around them, which range from potentially poisonous mushrooms to wildlife creatures that regard them with curious stares and as a potential meal. After a while you stop wondering how there could be four Sasquatches in the world — they’re supposedly mythical — and switch to wondering how there could be any Sasquatches at all, given their reckless behaviour. But it’s hard not to feel for these hirsute numbskulls as they get into increasingly serious dilemmas.

Nathan Zellner’s alpha male Sasquatch is the most foolhardy of the lot. He’ll eat anything, including overripe raspberries that appear to have fermented into natural moonshine, emboldening him into a mistake he’ll regret.

Eisenberg’s Sasquatch is more cautious and contemplative; he likes to count stars and tree rings. He might be the mate to Keough’s sad-eyed matriarch and Zajac-Denek could be their son.

We don’t know for sure and it hardly matters. A little bit of Bigfoot lore goes a long way (it really does get gross), but the beauty of “Sasquatch Sunset” is how it depicts humans as mysterious intruders in their world, not the other way around.

The human presence is indicated by red Xs on tree trunks, by faraway glimpses of swimmers near a shoreline and by a well-stocked campsite the Sasquatches discover, where a boom box plays the Erasure song “Love to Hate You.” (The rest of the music in the film is courtesy of Texas art pop band the Octopus Project, which conjures a soothing flutes/synths/strings soundtrack that could double as a meditation tape.)

The Sasquatches are so intimidated by humans that their discovery of a paved road prompts them to evacuate their bowels and bladders.

On second thought, that could be one of their rare flashes of intelligence: a commentary on the paving of paradise by life forms that are similarly heedless to their propensity for self-destruction.