Baz Luhrmann, writer-director of the adventure epic Australia, calls the decision his "biggest risk - by far, the biggest risk - in a film in which every risk was big".
Speaking from Rome, where he was premiering the $130 million historic action romance, which stars Nicole Kidman and Hugh Jackman, Luhrmann wasn't talking about any of the set pieces that lend Australia its larger-than-life scope and sweep.
He wasn't referring to the movie's cattle stampedes, its re-creations of World War 2 bombing raids, or even the movie's attempt to combine bodice-ripping romance with period Western while tackling issues of social injustice.
No.
Luhrmann's "risk" was casting Brandon Walters, who had never acted before, to portray Nullah, a central character around whom much of Australia is plotted and who also provides the movie's voice-over narration.
"I'm going to go hang the whole movie on an 11-year-old boy?" Luhrmann said, recalling the surprise at his decision among executives at the movie's distributor, 20th Century Fox.
"We could have had a wholesale rejection. Really, there was a lot of concern about it. A lot of, 'That's madness'. The studio doesn't ever ultimately battle me on anything. But after the first thousand boys we auditioned, they began to get nervous."
Turns out Luhrmann is hardly the only prestigious film-maker gambling on amateur talent these days.
Whether in pursuit of greater authenticity, out of sheer necessity or in the blithe spirit of stunt casting, a number of this season's more high-profile films feature novice actors in leading roles.
A boisterous pack of youngsters bring a hard-to-fake street verisimilitude to one of the year's best-reviewed films, Slumdog Millionaire.
And director-star Clint Eastwood hired a cast of Hmong-American teenagers, all but one of whom had never acted before, to appear with him in the provocative drama Gran Torino.
What distinguishes this new crop from the rank and file of indie-movie new jacks - i.e., the kind of untested actors hired because of shoestring budgets more than for the quality of their "work" - is context.
Cineplex screens have been crowded with amateur actors in independently produced festival winners and European hits such as Ballast, Gomorrah and The Class all year.
But nowadays, nonpros are turning up in studio-backed features with substantial budgets and share the screen with bona fide movie stars.
In other words, they are nabbing roles in the kind of films usually reserved for established screen names.
"You can use the fragmentary nature of film-making hugely to your advantage with inexperienced people," explained Danny Boyle, director of Slumdog Millionaire.
"You get a freshness with them that more than compensates for any technicalities you have to teach them. The compensation for freshness and directness easily outweighs any of that."
Gran Torino follows the story of Walt Kowalski (Eastwood), a take-no-bull Korean War vet grappling with a culture clash: his working-class Detroit neighbourhood has become populated by Hmong people, a Southeast Asian ethnic group.
But when Walt defies his racist tendencies to help out a teenage Hmong neighbour, he's thrown into conflict with a local street gang.
Wanting to cast people from the ethnic group but faced with a relatively scant pool of trained Hmong actors, Eastwood had casting directors conduct open auditions in cities with large Hmong populations.
"It's a very close-knit community," said Gran Torino casting director Ellen Chenoweth.
"They heard Clint was doing this movie and realised a lot of people don't know what Hmong are. They were so eager to have their story told correctly and be involved they embraced us and were very helpful."
Around 20 nonprofessional Hmong actors were cast.
Minneapolis high school pupil Bee Vang read about Gran Torino on a Hmong Internet discussion board, contacted casting agents and was asked to audition.
A novice actor, he was hired to play the movie's secondary lead, the neighbour Eastwood's character initially shuns before befriending him.
"It said, 'No experience necessary' on the ad," said Vang (17).
"When the camera first went on, it all came rushing to me: 'I'm here with Clint Eastwood, American icon.' It was not only scary, it felt like a dream."
Nonprofessional actors have appeared in movies since the dawn of film-making.
In recent years, amateurs such as Edward Furlong (Terminator 2), Brad Renfro (The Client) and Jason Statham (Lock, Stock and Two Smoking Barrels) went from never having acted to being "discovered" to parlaying a shot at fame in a mainstream movie into viable acting careers.
But in the past decade, the trend toward casting novices really gained traction.
After securing a $14 million budget and a distribution deal with Warner Bros for Slumdog Millionaire - which follows an impoverished street urchin who uses his romantic yearnings and a reservoir of arcane cultural savvy to go the distance in India's version of Who Wants to Be a Millionaire? - Boyle did not set out to cast a troupe of nonprofessional child actors.
Or, for that matter, to shoot the first third of the movie in Hindi.
But when Boyle arrived in Mumbai, India, where the romantic drama is set, and began to interview trained actors for the key roles of two orphaned brothers and a young girl from the city's poorest precinct, he found a certain physical verisimilitude lacking.
"In the morning, we'd be auditioning these middle-class kids who are fast-food eaters," Boyle said.
"And in the afternoon, we'd be going around the slums looking at locations. I'd be looking at the real kids. And they'd be completely physically different. The expression in Britain is 'wick'. They're wiry and quick. Alert. Alive. Survivors."
In addition to hiring local "fixers" in a number of smaller parts - and having Freida Pinto, a former model with no previous acting experience, as Slumdog's adult female lead - the director decided to cast real street children (three 7-year-olds and two 12-year-olds) in the protagonist roles.
Which led to further complications.
"The casting director, said, 'Seven-year-olds don't speak English'," Boyle recalled.
"A lot of the slum kids don't go to school."
The script was translated into Hindi and shooting commenced.
But the studio was less than overjoyed at Boyle's switch.
"Imagine it from a distributor's point of view," the director said.
"'It's going to be unwatchable! You're not going to be able to understand what anybody's saying!' But when you're there, it becomes all about the realism."
For Australia, to cast the central character Nullah, Luhrmann had casting directors scour the continent; he explained that there is no child casting agency that represents Aboriginal children in Australia.
The director travelled to 30 impoverished Aboriginal enclaves to audition children.
And after deciding upon Brandon Walters, Luhrmann went on an 11-day hunting expedition with the boy's father to persuade Walters' family that his intentions were honourable.
In dealing with novice actors, though, film-makers are bound to bump up against a certain lack of polish.
Like when the person you want to hire has no clue about who you are.
Discovered at a swimming pool in far-flung northwestern Australia, Walters was oblivious about his director and had co-star Nicole Kidman's stock-in-trade all wrong.
Asked if he knew who Luhrmann was before filming, Walters said: "Not really. My family told me he did Moulin Rouge and Strictly Ballroom. Nicole, I thought she was a famous pop singer or something."
Luhrmann laughed at the memory.
"At first, he was quite shy. Nicole really helped with the directing of him."
But in the writer-director's view, that guileless quality made Walters perfect for the role.
"He seems majestic, and he is," Luhrmann said.
