It would be difficult to approximate the ferocious sensation of the three boys running through the house exactly how they were described in Justin Torres’ coming-of-age novella “We the Animals,” but Jeremiah Zagar could feel the same exhilaration, not necessarily in reconnecting to his own youth, though there was that – but in how he tore through the pages of the book just after finding it in the “We Recommend” pile of his favorite bookstore in New York. He didn’t leave the cafe in McNally Jackson Books until he finished up the 144 pages, nor would he move for a few minutes after, his mind only gradually catching up to the feelings Torres would elicit in recalling a violent childhood in which affection and anger were expressed physically in equal measure.

Zagar had just come from wrapping up a film about his own family’s complicated history with “In a Dream,” a documentary that examined his parents’ tumultuous marriage as it reaches a breaking point, pieced together in such a way that it resembled his father Isaiah’s grand mosaics that line the streets of Philadelphia, and showing a gift for being able to convey how rough edges can fit together, he was the ideal person to realize Torres’ novel on screen, wrangling the author’s vivid prose into a continually unfurling, rambunctious chronicle of a three brothers and their parents Ma (Sheila Vand) and Paps (Raúl Castillo), seemingly living on the edge of the world in a home humble enough for them to afford. They make their own excitement, with the youngest (Evan Rosado) pouring his soul out into the personal journals he keeps, yet resists sharing everything with either his brothers or Ma and Paps, whose increasingly volatile relationship concerns him, though he’s too young to understand fully why.

Taking the unnamed boy’s point of view, “We the Animals” exudes a sense of wonder, but also uncertainty as the new experiences and emotions that he feels can feel as dangerous as they are exciting and Zagar makes the film explode off the screen, bursting with not only the vibrant performances from Vand, Castillo and Rosado, plucked from a year-and-a-half casting search, but with Czech-influenced animation to breathe life into the boy’s journals and Zak Mulligan’s dynamic camerawork throughout. Shortly before the Sundance favorite rolls into theaters, Zagar spoke about how he put it all together.

Raul Castillo and Evan Rosado in "We the Animals"What were your first conversations with Justin like?

It was really nice. He just is so smart, so insightful and clear-eyed and generous. It was clear just from that first meeting, we were going to work together and we were going to be friends and he was down to do something crazy. The book was wild, so the movie had to be wild and messy and dirty and alive and he was down for that. We always thought of the movie as a translation rather than an adaptation and that [meant] having the author involved as much as possible, so Justin watched the movie at every editorial stage. He was the primary consultant in the film. He made sure that everything was represented in a way that felt justified for the book. It was a beautiful meeting of the minds and I think it’s what makes the movie strong.

At Sundance, you had mentioned how there would be things in the book – like body heat – that would be a single line that you could extrapolate entire sections of the film from. What was it like finding those things?

We were always trying to figure out ways of communicating things that were in the book that we couldn’t put into words, so when you watch the brothers grow up in the book, there’s a very beautiful and long future tense explanation of their aging process. [We shot an ending five months after production ended, so you could] see those boys age [to a degree]. We wanted you to feel the seasons change. We wanted you to see their hair grow and what it’s like to go through puberty and to really see the difference in these young men was vital. But we [also] knew we had to find metaphors that were in the book that would express that visually and sensorially.

Body heat became a real metaphor for intimacy, and making it a poignant moment in the end was really us expressing that intimacy between the brothers was now lost. It was in the book, but it was just not in the book in exactly that way. It was the same with the animation – they talk about the boy drawing with the crayons, they talk about the journal, but [it wasn’t explicitly connected, so] we were trying to find ways of threading those motifs throughout the movie.

A scene from "We the Animals"How early did you have to get started with the animation?

There was always an element of [the boy] drawing under the bed, but we realized in editing that we weren’t enough in his mind, just seeing the pictures – that you had to see them come to life, you had to understand that they were a part of his life. And I used animation a lot in my first film “In a Dream,” so I understood that it could be a tool to get in somebody’s mind. We used it in the same way in that film and we brought on this incredible illustrator Mark Samsonovich, who actually hadn’t done much of any animation before, but he really got the essence of what this young boy’s drawings should be. Then we showed the animation to Justin and he really loved it as well, so from there, we knew it was going to be an intrinsic part of the story.

Did you have a strong idea of the edit in your head?

Yeah, a lot of the editorial stuff is preordained and a lot of it is not. We very much wanted to make a movie that had the same rhythms as the book, so our composer Nick Zammuto was involved in the process from the very beginning, even before we shot, and we always knew we were going to create these musical, rhythmic scenes that built [momentum] editorially. But because the film is a fever dream, the themes can move around. What you’re dreaming as an audience doesn’t have to be linear. So editorially, we had a lot of freedom to move a lot of scenes to different places and mostly the themes were preordained and the structure changed.

When you say you wanted the film to be wild, it seems like a lot of that was setting up the conditions and letting the cast loose. I can remember you saying for instance, you had the actors playing the brothers sleep in the same room on location. What was it like creating a reality for your cast that you could bring onscreen?

I think it was because I’m a documentary filmmaker and not a narrative filmmaker and I don’t actually know how to make a narrative film, I wanted to make it as much like a documentary as possible. [laughs] So if the boys were all living together and Ma and Pops were living together and we created an environment that was as real as possible, I figured that when we shot the scenes, they’d feel as real as possible. That was the ethos throughout. It was also the ethos for Zak [Mulligan] and I. Zack is an amazing cinematographer and he lit the scenes 360°, so the kids could do whatever they wanted to do. There were never specific marks that they had to hit. You could be wild and you could be free because the movie needed to be free, and there’s lots of little things that weren’t scripted and just happened, like the scene where the boys just [play] this game? Little things like that, because the environment was free, the boys could just start doing something and we could just film it. It was like thrilling and cool and fun.

A scene from "We the Animals"Was there a particularly crazy day of shooting on this?

Always. Every day. Every day I just assumed that everything was going to fall apart and we were going to go under. I felt like we were a sinking ship every single day and every single day I don’t know how we made it out the other end, but we did. We had this amazing acting coach named Noelle Gentile, who worked with the kids to make sure they could also be flexible within the scenes. And also, you know, Raul [Castillo] and Sheila [Vand] are so incredible – they’re not just naturalistic actors, but also such rehearsed, clear-eyed, practiced, trained actors that when the kids were watching them act, they could see what they could become and watching them work made them better actors for sure.

What’s it been like traveling with this?

It’s sad for me. That sounds strange, but I loved the process of making the movie and showing the movie is like a process of loss. It’s beautiful to see people respond positively to the movie. It’s moving. But the idea I’m no longer making it is hard, [because it’s] incredibly rewarding, but also, you have this sense of loss that you’re no longer working on this thing that gave you so much meaning.

It’s been in the works for five years. Did you know from the start that it would be such a big part of your life?

I always assumed it was going to take a really long time — all my films do. And the films I love do and I think narrative films really do take a lot of time. That’s just part of it. When you’re deeply passionate about something, you’re ready for the long haul and you want the long haul because when you’re working on something for a long time, it really gives you a sense of purpose and a sense of meaning.

“We the Animals” opens on August 17th in Los Angeles at the Landmark and New York at the Landmark at 57 West and the Angelika Film Center.