Ari Aster is diving into the world of a paranoid man on his way to visit his mother in his latest film, Beau is Afraid, starring Joaquin Phoenix. Aster and Phoenix spoke with us recently about what it was like creating the film and getting into character.

Aster said that his film has roots in his first film idea, Beau, a short he made early in his career starring Billy Mayo, an actor he had also collaborated with in the emotionally challenging short, The Strange Things About the Johnsons. Like Phoenix’s Beau, Mayo’s character is on his way to visit his mother until his paranoia takes over.

“I had just…graduated from, from AFI. I was in an apartment. I was about to move out of my apartment and I was moving out in three days and I just realized, ‘Oh, this is a location,’ you know, and those are hard to come by when you don’t have any money,” he said. “And so I thought, ‘OK, I’m gonna write something very quickly and it’ll be like an exercise. And I’ll get my friend Billy Mayo, who was in my thesis film at AFI and was just a really great actor. He’s died and he was way too young. And it was just a slap together [project]. And later on, just, this one part, like this one plot point in that short, kind of stuck with me–a guy leaving his key in the door and then, you know…going to get from, from the bathroom and then coming back, and the key’s gone. That stuck with me, and then it grew and, and I liked the name Beau.”

“If I had made it when I first intended to, I might have actually cast Billy Mayo at that time because it would’ve been my first film. I probably would’ve made it for absolutely no [money],” he continued. “The movie just kind of grew into something else. I don’t see this as a remake of that short or a, you know, um, or even really necessarily an expansion of that short….[T]he catalyst for the story is the same. But only to say that… this story has been just kind of growing and growing for me, and that character has been both growing and almost like turning more and more into like this enigma. The characters become even more enigmatic for me. I think a big question that Joaquin and I had was, how do we build this guy up and at the same time, retain, uh, like a mystery there and an unknowable [quality].”

Phoenix said that playing Beau was intriguing because of how much the character retains his goodness despite his environment.

“I mean, in some ways he’s awfully resilient. It’s incredible. Some of his good-naturedness, a kind of a sweetness, a goodness is relatively considering that he has been tested from his childhood and pushed to the brink. And I think that was something that was important for us to identify early on, like who was he when he was old? That was kind of our goal very early on was try to discover who that was.”

Aster also addressed why dissecting families in horror is so important to his work. As he said, we don’t have a choice in who are families are, “but you also can’t ever really detach from them.”

“…I think that’s a very interesting situation. And…I think chosen families are very interesting and I think that those are usually a response to the family you’re going into,” he said. “I don’t know, it just feels to me like an endless thing…I think it would be hard to find work that isn’t engaged at all [in] those questions. I know there’s a preoccupation for me, but it always feels to me like the obvious place to start.”

“…[N]ow that you ask it, I’ll, I’ll never do it again,” he joked. “I need to get away from [it]…I’m just spinning my wheels at this point.”

Beau is Afraid comes to theaters April 21.