VENICE, Italy (AP) - Viggo Mortensen and Kodi Smit-McPhee play father and son on a harrowing and hopeless journey in the film adaptation of Cormac McCarthy's devastating novel "The Road," premiering Thursday at the Venice Film Festival.

The movie, like the Pulitzer-prize winning book, is bleak, a search for hope where there appears to be none, but the relationship between the two actors is anything but.

Smit-McPhee plays a boy born in the wake of a cataclysmic event that has made life on earth unsustainable. Something akin to nuclear winter has set in: The sky is impenetrably gray and the air is cold. Food of any kind has become an extremely rare commodity, creating desperation. Some who survive, many it would seem, have turned to cannibalism.

It is against this backdrop that father and son set out on a journey toward the sea, their version of hope.

Preoccupations of the world as we know it don't matter. Neither father nor son are named. The cataclysm itself is never explained, because, as director John Hillcoat points out: "There were no more media linkups to explain things." Nor is it clear how long it has been since the world began to end, leaving the boy ageless.

"The Road" also stars Charlize Theron, appearing in flashbacks as the boy's mother, and Robert Duvall as a fellow survivor treading down the same road.

Smit-McPhee was 11 when he shot the film, 13 now, but he speaks like someone working the trade for years. As he has. His father is an actor who has coached his son, who by now has appeared in eight productions.

The young Australian actor, who pulled off a perfect American accent on screen, said his key to the most emotionally difficult scenes was to stay in the moment - a characteristic that won the admiration of 50-year-old Mortensen, who won fame as Aragorn in the "Lord of the Rings" trilogy and an Academy Award nomination for his performance in "Eastern Promises."

"That's what my dad told me when I first started acting, just be real, be in that moment. So if you don't know the world, you don't know the world and you just have to block it all out," Smit-McPhee said, referring to his character. "I didn't know what a padlock was."

In one pivotal scene after the pair reach the sea, the boy lets his father know that he shares the burden of their survival, dissolving any illusions the father had that he was protecting his son. Hillcoat's direction was to be emotional, but Smit-McPhee said that wasn't working.

"You were getting angry," Mortensen recalled during a joint interview with the co-stars, where the easy rapport that developed while filming "The Road" was evident.

"I thought: 'I am just going to do it angry,' " Smit-McPhee continued. "Just let me do it angry."

"That's being quick on your feet," Mortensen said. "But a lot of adult actors would never have figured that out. They would have gone home to the hotel and said, 'Oh, I could have just been angry.' But you did it there. Under pressure."

Mortensen's admiration was uncontained. "I can't think of any other actor of any age who is as present, which is the first thing to be in you job."

Then, turning to Smit-McPhee, he said: "You will keep working and improving, but you have an ability to focus and relax and be in the moment. I remember Robert Duvall, one of the first things we had to do with him, he turned to me and said: 'Where did we get the kid.' He was very impressed, immediately. ... I think he recognized a kindred spirit."

At other times, Smit-McPhee took physical cues to get the reaction he needed. Early in the film, the boy dissolves in tears, making him seem even smaller and more vulnerable, after his father rinses the boy's hair in cold water to clean out the blood and guts of a man the father has shot protecting the boy. It helped, the young actor said, that the water was freezing cold, the temperature measuring "minus a lot."

"I don't know if you can imagine minus-a-lot water on your head," Smit-McPhee said.

Mortensen and Smit-McPhee recounted with enthusiasm a day when McCarthy came to the set with his own son, a year younger than Smit-McPhee.

"I remember he came that day and he said, 'This is how I imagined that. And that was awesome," Smit-McPhee said with emphasis.

The two have an idea for a sequel that seemed to be based mostly on the multilingual Mortensen's nascent ability to speak Norwegian and Smit-McPhee's interview outfit: black trousers, black dress shirt and a red tie. "It is a Norwegian ghost story. It is called 'The Road to Resurrection.' I come back as a Viking ghost and he's in the Italian mob," said Mortensen.

That may be more appealing to Smit-McPhee's peers than "The Road." He doesn't think kids his age would like it very much "unless they are deep thinkers."

A shout out to a kid who lives across the street from Smit-McPhee: He thinks you qualify. But otherwise: "It's a hard sell," the young Australian said. "They would think it is cool about the cannibals, and stuff."

"The Road" is in the running for the Sept. 2-12 Venice Film Festival's coveted Golden Lion.