Viggo Mortensen and Kodi Smit-McPhee have eaten bugs together. They've shivered through frigid winter air, fought off desperately hungry cannibals and walked side by side on the empty and dusty roads of some future, dystopian America.

So when the two actors, separated in age by nearly four decades, recently settled into a decidedly non-dystopian hotel suite at the Toronto International Film Festival to recall these challenging film experiences - which they faced while playing a father and son fighting to survive, in The Road - they did exactly what you might expect.

They got really, really sarcastic.

Reporter: I sense there is still a father-son bond that exists between the two of you. Can you talk about that?

Mortensen: [Gestures to Smit-McPhee.] You start.

Smit-McPhee: Okay. [He gestures to Mortensen.] He sucks.

Mortensen bursts out laughing.

Reporter: You both had to go to some tough emotional places in this movie. How did you turn that off once the take was done?

Mortensen: He'd tell me I sucked.

Smit-McPhee: Then he went back to his room and had a cry.

Even in their smart-alecky moments - actually, especially in those moments - it's clear how much Mortensen, 51, and Smit-McPhee, 13, genuinely like each other. And that connection helps to elevate The Road, the long-awaited adaptation of Cormac McCarthy's Pulitzer Prize-winning novel, above Hollywood's parade of world-turned-hellish-nightmare movies. The two actors - one an Academy Award nominee (for Eastern Promises) and star of one of the most successful franchises in film history (The Lord of the Rings), the other a young Hollywood newcomer from Australia - manage to convince the audience that they really do share the same bloodline.

"Everything depended on that relationship," says Road director John Hillcoat when asked his goal in casting his two leads. "It's a love story between a father and son, and they're in every scene and go through every kind of emotion, so that was quite daunting."

As Mortensen put it: "My character absolutely doesn't work unless his character works, and vice versa."

Originally, Mortensen expected to draw on his feelings about his own son - Henry, now 21 - to inform his take on a father desperate to keep hope alive for his only child.

"That's how I connected to the book, and when I spoke to Cormac McCarthy before we started shooting, that's what we talked about," he says. "His kid. My kid. Being dads. But once we got going, it was really about Kodi and I going on this trip together."

Smit-McPhee is an unknown commodity to most American moviegoers, though a few may recognize him from his role as Eric Bana's son in the film Romulus, My Father, a part that earned him an Australian Film Institute Award. After Hillcoat looked over what he describes as "thousands" of young actors, the youngster from Melbourne managed to distinguish himself with a little help from his real-life father, actor Andy McPhee.

"There were certain scenes I would never have asked a kid to audition for," Hillcoat says. "Yet they did these extra scenes where his real father played the father in the audition tape. And that to me was a message that, you know, 'my son can handle this.' Or, conversely, that these people are absolutely insane and it's time to bring in child services."

With Smit-McPhee's commitment firmly established, the youngster (he was 11 when shooting commenced) and his co-star focused on getting to know each other. On the set, Mortensen taught the boy a few of his sword moves from The Lord of the Rings. Off the set, the two hung out around the Pittsburgh area, where much of the movie was shot; during our interview, they went off on a nostalgic tangent for several minutes, recalling an unusual church they explored, a local heavy-metal musician who tried to give both of them cigars and a shop where they sampled chocolate-covered crickets. (So, yes, they actually did eat bugs, both in and out of character. Smit-McPhee's verdict? "They tasted really good.")

But according to Hillcoat, their relationship took a more meaningful turn when they shot a scene in which Mortensen's character cleanses blood from his son's face by dunking his head into an icy stream. With the camera rolling, Smit-McPhee started to cry. It quickly became obvious to Mortensen, the crew and Smit-McPhee's father, who has a small part in The Road and happened to be on the set, that the boy's sobs were of genuine pain. Still, the two remained in character - and Mortensen continued to cradle Smit-McPhee in his arms - until Hillcoat said cut.

Smit-McPhee's "father did a very courageous, brilliant thing, which was to step back and let Viggo keep embracing him and comforting him to the point where he completely calmed him down, and then got out of him what happened and talked about the whole thing," the director recalls. "From that point on, it created a whole new - there was kind of a bonding experience."

After guiding the boy on their grueling, shared journey in The Road, Mortensen also seemed proud to usher him along another path: the one that leads to a long-lasting career in Hollywood.

"I think it's good, when you can, to be patient," Mortensen said at one point when asked about how he chooses his parts. "And I think Kodi's being patient. He's trying to find roles together with the advice of his parents, particularly his dad."

"I've learned not to work with you again," cracked Smit-McPhee, again in sarcastic teen mode, mock-rolling his eyes.

"There you go!" Mortensen said. Then he smiled a proud-papa smile: "See what I mean? You learn a lot in this business if you want to, don't you?"