Viggo Mortensen and Kodi Smit-McPhee portray father and son in the harrowing survival tale The Road, but appeared more like a pair of wise-cracking pranksters at the Toronto International Film Festival on Sunday as they unleashed lighthearted barbs at reporters.

The comfortable rapport between the young Australian and the seasoned Mortensen was on display as the duo described pre-production bonding activities, including a visit to an anatomy exhibit that featured real human bodies and a trip to a Mexican restaurant in Pittsburgh to sample edible crickets and worms.

"We had to like each other, otherwise it probably wouldn't work out that well," said Smit-McPhee. "But I think because Viggo's so nice we got along really well and we've been friends ever since the start of the film."

It wasn't long into the news conference before the mischievous 13-year-old switched the paper name plates that sat in front of him and his co-star so that he would be identified as "Viggo Mortensen," and Mortensen as "Kodi Smit-McPhee."

Later, the pair unabashedly colluded on how best to handle a reporter's question when asked what was Mortensen's favourite role.

"That's the oddest question ever," Smit-McPhee said in a quiet voice caught by the microphone in front of him.

"You hate that question?" Mortensen asked as Smit-McPhee nodded.

"What do you say when they ask you that question?" asked Mortensen.

"All of them," the exasperated youngster replied.

"Yeah, that's what I'm going to say," Mortensen agreed.

Later, when Smit-McPhee was asked how he felt when he read the Cormac McCarthy book the film is based on, he smugly replied: "I guess the same as it made you feel when you saw the movie."

"That was a good answer," he said, turning to a laughing Mortensen.

Sunday's lighthearted banter stood in stark contrast to The Road's bleak storyline, in which an unnamed father and son wander through a post-apocalyptic landscape searching for food, dodging thieves and hiding from cannibals.