“Sasquatch Sunset” may be the weirdest movie you've ever seen.

Where to begin?

Well, the film (in select theaters now, expands nationwide Friday) imagines the lives of a family of Sasquatches (aka Bigfoot) over the course of four seasons. The dialogue consists of grunts, moans and howls, and some scenes of Sasquatch sex and scatological pranks. For 90 minutes.

“Sunset” plays like a National Geographic project, albeit about a mythical creature that has parallels in other cultures, such as the Yeti in Asia and Chupacabra in Mexico. The movie's authentic look is the result of a deep dive by filmmaker brothers David and Nathan Zellner into the online Bigfoot fan community. No snickering, please.

And while the documentary-style movie – which ably melds pathos with comedy − stars Jesse Eisenberg (“Zombieland”) and Riley Keough (“Daisy Jones & the Six”), don’t count on recognizing them under layers of Bigfoot makeup.

In fact, Keough says, when she saw Eisenberg at the movie's Sundance Film Festival screening in January, “I felt I was meeting him for the first time, because I never saw his real face. We’d get to the makeup trailer and put on our Sasquatch faces and that’s all we ever saw.”

The Zellners as well as Keough and Eisenberg shared their thoughts with USA TODAY on crafting this unique cinematic experiment, which feels like a midnight cult film in the making.

What was the inspiration for 'Sasquatch Sunset'?

In 2011, the Zellners released a short film called “Sasquatch Birth Journal 2.” The hook was set. They spent the next decade crafting a feature-length script and securing funding from skeptical investors.

“Most Bigfoot movies were either family fare, like ‘Harry and the Hendersons,’ or just horror movies, and we felt there was a film in there from the creature’s point of view,” says David Zellner. “OK, it’s not likely what people are asking for. But we hope people enjoy it.”

Nathan Zellner also stars as one of the Bigfoot creatures. “I guess I have the build for it,” he jokes. “But, yes, David always had me in mind to play the brooding alpha-male giant. It was like wearing the best Halloween costume ever, for a month.”

How long did it take for the cast of ‘Sasquatch Sunset’ to get into makeup?

Eisenberg, 40, and Keough, 34, agree on the best costume part, but perhaps don’t share their castmate’s enthusiasm for being entombed in the garb, which Eisenberg says took nearly two hours to put on.

“Imagine glue on every part of your face, then prosthetics, then hair,” he says. “The amazing thing is we do all kind of look different and a bit like ourselves. But I have never done anything as taxing and excruciating as this movie. Walking 20 feet was brutal. They’d say, ‘OK, now lift this leaf,’ and you’d be like, ‘I need a break.’ ”

Keough says she had to “meditate and center myself” before the shooting day began. “Walking to the bathroom alone, you were just giving up,” she says, laughing at the memory. “I thought I was truly going to collapse. We sound like babies, but it was really challenging.”

How did David and Nathan Zellner create their Bigfoot world in ‘Sasquatch Sunset’?

Beyond the realistic makeup, which took its cue from infamous grainy 1967 footage of an alleged Bigfoot in what was dubbed the Patterson-Gimlin film (which the movie nods to in its opening sequence), the Zellners visited websites dedicated to Bigfoot lore.

“On YouTube, you’ll find people showing piles of branches that they believe are Sasquatch nests, or twisted sticks that they think are Sasquatch glyphs, and other people talking about burial rituals, so we just borrowed from all of that,” says David Zellner.

Lending further realism was the choice to set the monthlong shoot in dense Northern California forests, supposedly the home range of Sasquatch. “The location was perfect, but also tough,” he says. “We dealt with extreme weather, we shot with only natural light. There was nothing controlled about the environment, but hopefully that gives the film its ‘70s nature-doc look.”

Why was making ‘Sasquatch Sunset’ so freeing for Riley Keough and Jesse Eisenberg?

In one of the movie’s most outrageous scenes, the Sasquatch brood gets upset and starts throwing its excrement. Standard ape behavior, but not so common for humans. And yet, enacting those scenes was wildly liberating, Keough says.

“I don’t find body humor funny normally, but when I read that scene on the page, it was just so funny,” she says. “I loved it all, it was the experience I’m always searching for when acting, total freedom in a character, no self-consciousness.”

Eisenberg echoes that. “This is something you’d do in an acting class, but never in a real movie, it’s just so experimental. There are scenes as hilarious as you’d find in any movie, and emotional ones, too.”

When Eisenberg's Bigfoot character is suddenly imperiled, the actor's wife, Anna, could not contain herself at the premiere. "She was literally weeping," says an incredulous Eisenberg. "And she’s never wept for me!”

Did 'Sasquatch Sunset' sway Riley Keough or Jesse Eisenberg that Bigfoot is real?

So did making “Sasquatch Sunset” convince either actor that Bigfoot might exist?

“I hope there’s at least one out there,” Keough says. Eisenberg is more philosophical: “I’m an angry skeptical person from downtown, but I love how the Sasquatch mythology represents a need to get back to nature.”

What did real apes think of 'Sasquatch Sunset'?

Though Sasquatch is likely to remain more myth than reality, the way the creatures are portrayed in this film evoked a strong reaction from a few Bonobo apes who saw it when the filmmakers consulted with primatologists.

“One of them in particular was watching, just really engaged, and then he casually lifted up his hand and smashed the (TV) screen as hard as he could,” Eisenberg says. “I guess that was his way of trying to dominate the creatures on the screen. But I’ll take that as one huge opposable thumbs-up for us from that community.”