Joaquin Phoenix laughed hysterically every time he saw Beau Is Afraid costar Nathan Lane

In Beau Is Afraid (out April 21), Joaquin Phoenix plays a stressed-out individual, living in a nightmarish part of an unnamed city, whose quest to visit his mother (played by Patti LuPone) turns into a picaresque phantasmagoria filled with bizarre and unexpected terrors.

"In a way, it's unclassifiable," says Phoenix's costar Nathan Lane of this third film from Hereditary and Midsommar writer-director Ari Aster.

Lane and Amy Ryan portray Roger and Grace, a seemingly normal, suburbia-dwelling couple who take in Phoenix's Beau after running him over.

"I play this lovely woman named Grace, who hits Joaquin Phoenix with her soup van-truck by accident, or by accident on purpose," says Ryan. "She has so much guilt that she takes this grown man home, and puts him to bed in her teenage daughter's room, so he can recover from his wounds. Luckily, Grace is married to a star surgeon named Roger who's going to really stitch him up and get him on his way."

In addition to their "troubled" teen daughter, as Lane describes her, Roger and Grace also have a son who died in war. "He seems very upbeat. There's a lot of dad humor, he's a bit corny, but very positive about everything," Lane says of Roger. "Yet, underneath it, there's something sinister at play. Things are not what they appear to be."

Lane concedes that the creative discussions between Aster and Phoenix threatened to reach boiling point at times during the shoot, which took place in Montreal.

"[Joaquin] and Ari would have very intense conversations about what they were doing, and why they were doing it," says the actor. "If it got heated, Joaquin would always come to us and say, 'We're sorry, we love each other, he's my brother, we're just so passionate about this.' They're great artists, and they also are just very lovely, kind, compassionate people, and so it was a great experience."

One thing that could break the tension and always put a smile on Phoenix's face? The sight of Nathan Lane!

"He couldn't look at Nathan without laughing," says Ryan of the Joker Oscar winner. "And I don't mean giggling, I mean hysterically laughing. The cameras are getting ready, and sound is speeding, and Joaquin, he can't keep it together. I thought, oh my God, we're never going to get this scene done. But, in some inhumane nanosecond, it drops away, and he is in that character. So, from my experience working with him, my perspective, he's not one of those actors who needs to stay in this character for extended periods. He is so dialed-in that he can have this genuine, raucous, hilarious moment with Nathan and me and whoever else on set, and then, in a tenth of a second, he's in the scene."

Lane and Ryan saw the finished, three hour-long film together.

"Nathan came into the screening with a giant thing of iced coffee," says Ryan. "My first impression was like, 'Oh no, you're going to miss part of the film! There's a long way [to go] to have that big an iced coffee!' I laughed a lot, even having known what was coming up, but there was so much humor, little details, and jokes. Also, we're in this film, but we barely saw the other actors in the other chapters, so it was gratifying to see how the film went on past us. It made me dizzy. We went and got a meal afterwards, and we talked it through, because there was so much to unpack. It kind of stunned me."

"I loved it," says Lane. "I don't know what other people will make of it. Look, this is for serious moviegoers. This isn't a frivolous diversion, this is a challenging arthouse film, and it asks something of the audience, and it throws a lot at you. You're getting, really, a man's entire life. I love that it's out there, and playing with the form, and telling this epic tale."

The cast of Beau Is Afraid also includes Parker Posey, Richard Kind, Zoe Lister-Jones, and Stephen McKinley Henderson. The A24 film opens in New York and Los Angeles on April 14 and nationwide on April 21.

Watch the trailer for Beau Is Afraid below.

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