"E's a monster," David Cronenberg whispers dramatically. "I'll deny I said that when he gets here." We are awaiting the arrival of Viggo Mortensen, star of Cronenberg's new movie, Eastern Promises, out Sept. 14, as well as of his previous film, A History of Violence. In both of them, Mortensen does, quite convincingly, play characters with the potential for monstrousness.

Eastern Promises finds Mortensen playing Nikolai Luzhin, a Russian ex-con tattooed from head to toe with elaborate designs detailing his every misdeed and prison stint. He puts out lit cigarettes on his tongue, can fight to the death while naked and has a knack for snipping the extremities off corpses to make them more portable.

So it's a little underwhelming when Mortensen walks in and starts bustling around, brewing up a pot of herbal tea and assembling a lovely plate of fresh berries. He and Cronenberg banter like a pair of spouses, which the white-haired director says is pretty close to the truth.

"I love Viggo - it really is a collaboration," Cronenberg says. "It's like a marriage. You might see two people together and not understand why they are, but they know. We know. We feel we can get the best out of each other."

Of course, the question of what this director considers "the best" is a hazy one. His movies are known for probing the darker, often gorier sides of the human psyche - Jeff Goldblum's transformation into an oozing human bug in 1986's The Fly, Jeremy Irons' off-the-rails twin gynaecologists in 1988's Dead Ringers and James Spader's car-wreck fetishist in Crash.

He's got a flair for the gut-wrenching and the visceral and, like it or not, images from his movies tend to linger in your head long after you've left the theater.

This time around, the scene that will have everyone talking is the Russian bathhouse fight, in which Nikolai is attacked by two leather-clad, knife-wielding thugs - while he's sweating it out in the sauna with only a towel slung over his shoulders.

"As we started to work the scene out, Viggo said, 'Obviously, I have to do this naked, because that's what would happen,'" Cronenberg recalls. "He was aware that if I had to worry about how to shoot it - about not showing any nudity, or anything from the waist down - it would be incredibly restrictive. It would, in fact, be the antithesis of what I wanted do in that scene, which is to have it flow so you could see the actual physicality of it."

"That's the thing I liked about the way David shot that scene," says Mortensen. "Everything that happens is necessary and practical. There's no wasted, fancy moves just to call attention."

"Killing someone with a knife or a blade is a weirdly intimate, almost erotic thing," the director muses. "And if the knives are really short, it's even more so. You have to get very close to do something like that."

The link between violence and sex is one Cronenberg also explored in A History of Violence, in which Mortensen's character, a mild-mannered family man, is discovered to have a hidden past as a highly skilled killer. But despite the surface links between the two, Cronenberg says they're not intended to be companion pieces.

Eastern Promises does, however, contain the fascination with body imagery that runs through all Cronenberg films. Both director and star did extensive research on the tattoos that would tell Nikolai's story, determining whether he'd be allowed into the London branch of the Vory v Zakone, a Russian mafia brotherhood.

"In prison," Mortensen explains, "they'd be checking out the tattoos to see if you actually earned what you're wearing. And if they find out you didn't, they'll say, 'That tattoo on your arm, you didn't earn that - we'll give you an hour to get rid of it.' So you're either going to have to cut it out or burn it off. And if you don't, they'll come back and beat you nearly to death, and then do it for you."

Yeesh. Clearly, he's got a good grasp of the kind of detail that makes Cronenberg sit up and take notice. In fact, the director says, he didn't even need to dictate prep work for his actor - Mortensen just knew. "I phoned him and I said, 'I'm reading this new translation of Dostoevsky's The Possessed, I think you should read it," says the director. "And he said 'I just finished it' - that same translation!"