Robert De Niro, Edward Norton on their ‘Stone’ work

As they sit next to each other in a Toronto hotel, Robert De Niro and Edward Norton make an odd pair. A few hours before the premiere of their movie “Stone” at the recent Toronto International Film Festival, Norton sports a dress shirt and slacks, De Niro a blazer paired with cargo shorts and open-toed sandals, like a news anchor whose business attire ends at the waist. Norton is voluble, a self-styled intellectual ready to clarify his answers with citations from De Tocqueville, where De Niro’s conversation is riddled with gray areas and no-go zones.

Although De Niro is notoriously reluctant to do interviews, and often tight-lipped when he does, he’s relatively loose in Norton’s company. At times, their exchanges are playfully barbed, as when Norton addresses the subject of his own reputation for sharing his opinion on set.

“I battle sometimes,” Norton allows. “Sometimes, I’m probably a little bit compulsive.”

De Niro smiles, his eyes softening. “They had a couple of two-hour conversations while I was waiting,” De Niro says of his co-star and director John Curran.

Norton shoots back, quickly enough to suggest they’ve kidded on the subject many times before. “Sometimes we’d have a two-hour conversation because Bob would be on the phone, and we’d have nothing to do but talk about where to put the camera.”

In “Stone,” which opens Friday and reunites Norton with his “The Painted Veil” director, De Niro plays a prison counselor assigned to interview Norton’s convict and determine whether he’s ready to be paroled, meaning that he accepts responsibility and feels remorse for his crime. The natural thing, the expected thing, would be for Norton to claim he’s learned the error of his ways, whether or not he truly has, but instead their sessions are verbal sparring matches, confrontations with the sustained intensity of a stage play.

Although he affects an air of moral rectitude, De Niro’s character is at least as compromised as Norton’s felon. In the film’s opening sequence, where a young De Niro is played by “Dollhouse’s” Enver Gjokaj, he responds to his wife’s threat to leave him by holding their daughter out a second-story window. The tension is amplified by the furious buzzing of a bee along the sill, an introduction to a movie in which sound plays a key role.

The score by Jon Brion, who added the anxious drums to “Punch Drunk Love,” is enhanced by ambient rumbles contributed by “ Radiohead’s” Thom Yorke and Jonny Greenwood (the latter also contributed the screeching glissandi to “There Will Be Blood”) and ominous sound design by veteran Skip Lievsay, who worked on “No Country for Old Men’s” unsettling soundscape. Late in the game, Norton’s character claims to have experienced a religious conversion courtesy of an invented religion called Zokangor, in which the spirit enters the body through sound. It’s easy enough to imagine, since by that point the movie’s aggressive sonics have all but drilled holes in your skull.

“Stone” marks the first time Norton and De Niro have collaborated since 2001’s “The Score,” but they kept in touch between the two films, and in a more serious moment, it’s clear that De Niro prizes his younger colleague’s polymath talents.

“One thing with Ed that I’ve liked when we’ve worked together, he always has a lot of ideas,” De Niro says. “He’ll rewrite stuff and that’s always great because he’s very much committed to the project and involved. As far as I’m concerned, that makes it easier for me in some ways.”

“For me, the second time around with anybody is better,” Norton says. “Even if you already know somebody, everybody’s got a different rhythm, the way they work. When you go through that once with someone, it’s just easier to go, ‘Yeah, I know how we roll.’ You get an unconscious shorthand going. I felt that definitely, even in some ways more, with John. Bob’s worked with many directors multiple times, and to be honest, I’ve always looked at that relationship from afar and thought how nice that would be, given how much work it is each time you start on a film with someone you’ve never worked with. I really liked doing it a second time with John, because I know everything about how this guy works. There’s so much less debate.”

That’s not to say the production was free of disagreement. Although he was intrigued by his character, De Niro harbored unanswered questions about him that he is still unsure the film answers. (At the time, he had yet to see the final cut.) “It was like a puzzle,” he says. “I wasn’t sure about certain things because I didn’t know whether it was clear enough, whether it was visceral enough. I didn’t know whether an audience could feel why just because of that beginning scene. It was all for me very muted and subtle in a certain way, which is what it was. It’s OK. It’s just I thought because it’s like a morality tale that it had to have a real biblical payoff. But it was a director’s choice, and in a certain way Ed’s choice.”

Although Norton is credited only as an actor, he describes being involved from pre-production through scoring sessions, enough to take an evident sense of ownership in the final product. He doesn’t interrupt as De Niro voices his reservations, but he coughs sharply during one of the elder actor’s pointed critiques, the rest of the time staring out the window and brushing his fingers over his eyebrows. Once De Niro has finished, he jumps into the fray.

“I find myself less and less interested in movies that just tie it up and deliver it to you and let you cruise out going, ‘Oh, they wanted you to take away this message,’” Norton says. “I don’t think that actually engages people’s brains that much. When I think about movies that stuck with me, I like the ones that leave a lot of questions in your mind. I like leaving the questions open.”

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