Edward Norton and Tim Blake Nelson came to Dallas recently to talk about their new movie “Leaves of Grass,” a comedy about twin brothers, marijuana and existential dread that Nelson wrote and directed and Norton co-produced and stars in, in his first double role as the brothers—Brown professor Bill and redneck Brady.

“I wanted to write something funny, but because of what was going on in my life, I also wanted to write about that,” Nelson said. “The initial conceit was just a guy examining his life, trying to live in all the right ways, who gets completely sideswiped. That evolved into him being a professor of classical philosophy and being sideswiped by his perhaps more brilliant identical twin brother, who grows hydroponic pot back in their home state of Oklahoma. And then I started thinking of Edward in both roles, and just had a blast writing it. I did feel that the American people needed a film about philosophically contrapuntal identical twins. The tide was just going that way, and I’m surprised I was the only one to have recognized it. There have to be trail-blazers.”

How difficult was it to manage the scenes in which Norton played both brothers in scenes? “We’ve come a little way since Patty Duke,” Norton joked. “Effects technology have advanced gorgeously, as anyone who’s seen ‘Avatar’ or any blockbuster movie can attest,” Nelson added. “And that’s certainly true with simple special effects, like a single actor inhabiting identical twin roles. Now you can move the camera, and have the characters walk in front of one another, and we used techniques on an ad hoc basis. There’s motion-control photography, where a computer will memorize a dolly move and then repeat it for Edward twice. In post-production you do what’s call rotoscopy, which involves placing a character inside of a moving shot. And then we did poor-man’s process—simple splits down the middle, and compositing in post-production, as well as shooting over a double wearing a wig.” Norton interjected, “The high and the low…”

“But while I’m really proud of what we did technically, it would all be meaningless without the soul of Edward’s performance,” Nelson emphasized. “He’s such a truthful and generous and meticulous actor. And all of the technical wizardry would be pretty meaningless. The real heartbeat of the movie is the really human approach that Edward brings to these two characters.”

Norton addressed the issue of playing the twins. “It was a fun challenge, a different thing than I’ve done before,” he said. “Technically, we knew it would be a jigsaw puzzle, a weird dance that we’d have to figure out. There’s antecedents of it in early drama, Shakespeare and the Greeks have these mismatched twins, and I liked that it pulled on old traditions of a certain kind of story, and I thought that taking that old archetype and retelling it as a bridge between Little Dixie and the Ivy League seemed so fresh to me, and original. When I read it I just thought that more than anything, more than even playing the twins, it was not a movie I had seen before. Ninety-eight percent of scripts are derivative of something that I’ve seen many times before, so when you get the sensation that this will feel new, that’s worth a lot to me.

“You can to treat two characters the same way you treat one character, but at the same time, the technical fun in it for me is that the technical stuff will give you a lot of support, but we had to work on ways to buff the scenes out. I think unconsciously people start to look at the technique if it’s going Ping-Pong between the lines. You have to figure out the ways that conversations and people in space together are actually messy. The unconscious cues to the audience that two people are in the same space are overlapping and interrupting and interactions between body space. It’s all these little things that, without them, you get pulled out, but with them, you don’t really notice them, but you stay in your suspension of disbelief. Coming up with how to make two people’s conversations seem extemporaneous is clever and fun.

“It was the mix of the two that was really fun. It was like being both Abbott and Costello—the funny guy and the straight man as well. Any of the scenes with the two of them together we had to do in the same day. It was fun to let Brady blast and then watch Bill react. Playing a character like Brady is a lot of fun, but I really think with characters like Bill, whose life is coming off the rails or going on tilt, there’s some really funny stuff in that. With Bill you have to come up with about eighteen aggrieved reactions.”

Nelson also acts in “Leaves of Grass,” playing Bolger, Brady’s loyal, laid-back colleague in the marijuana trade. “When I read it, maybe just projecting too much assumption of actors and our narcissism, I just assumed that if he wrote my part, then he was writing one for himself too,” Norton joked. “And as I was reading it, I couldn’t imagine anyone else as Bolger. He, being disciplined, was thinking maybe I should, maybe I shouldn’t, but our other producing partner and I basically took away the option of him not doing it—it was too perfect.”

“Leaves of Grass” alternates between gentle humor, slapstick, drama, and even violent tragedy—variety that Norton appreciated. “I like films that don’t fit into a neat box,” he said. “I like films that are funny and disturbing, or funny and touching. There are so many films that achieve more than just one sort of interaction. I thought Tim’s film was very ambitious. When you start with a lecture about Greek philosophers and how what they had to say is still relevant, that’s ambitious, when you’re starting out to shoot crossbows through people and stuff. I think those kinds of ambitions make for better-than-average films.”

“We all have forces and conflicts within ourselves,” Nelson explained. “So by being very specific in this movie about my own, I’m hoping that it will speak to others. There’s the adage that you find a very tiny corner of the world and write about that to reach the universal. That’s what we’re after.”

“I’m proud because I think we’ve made a very daring film,” Nelson emphasized. “I was never interested in doing just a pot comedy. I like them, but that’s not what I was going to spend two years doing.”

“Seth Rogen does it so well. There’s no reason for us to aim at that,” Norton joked.

“I’m interested, particularly in this movie, not just in the longitudinal progression of a movie—the straight narrative—but I like latitude as well,” Nelson added. “I think the most interesting movies take those sorts of chances. And so the notion of having really comic moments followed by suddenly very violent ones makes for a more daring, interesting film, and frankly a film that’s more empirically in tune with the subject matter. Because this movie about ‘how do you live life’? And life certainly isn’t only funny. And we’re ambitiously examining it all here, I think without pretension. And when it’s without pretension, that means it’s organic while being unpredictable and never preachy. And that means stuff’s got to happen. And stuff happens in this movie—you can never get ahead of it. I’m proud to be in a tradition that takes chances.”

Norton and Nelson came to Dallas directly from Austin, where they’d screened “Leaves of Grass” at the SXSW Festival. “It was so great—it was like a dream,” Norton enthused. “There were laughing at noodling jokes, and at epistemology jokes.

“We were in the perfect spot.”