One of the last stops in the search for a boy to play Chow's rambunctious son, Dicky, was in Ningbo, a seaport town in the northeastern Zhejiang province, where the casting agents finally found their boy, who, as it happened, was a girl.
What was it about Xu Jiao, now 11, that made Chow believe she could play a boy?"I think it was a director's instinct.
There was something about her that grabbed me," says Chow, whose CJ7, pays homage to Steven Spielberg's ET: the Extra-Terrestrial.
"It's hard to put my finger on it," he says through a translator.
Chow (Shaolin Football, Kung Fu Hustle) plays Ti, a poor widower who works long hours at a construction site so he can send Dicky to a posh school.
Ti scours the local junkyard for useful items (including his son's clothes and shoes) and comes across what he thinks is an odd-looking toy that he brings home for the boy, who names it CJ7.
It soon reveals itself to be something else entirely.
Making her screen debut, Jiao is a charmer as Dicky.
She never had acting aspirations, she says through a translator as she relaxes in a room at the Beverly Wilshire Hotel.
"Los Angeles is just beautiful; I have the urge to go swimming here," she proclaims.
She is poised and funny as she tells about how her art troupe - in which children are taught songs - met the film's assistant director, who shot footage of them introducing themselves.
"They came back and wanted to interview me," she says.
Jiao, who sports cropped hair, sky blue fingernail polish, pink Nikes and carries a purse decorated with a little mouse, has an older brother, but he didn't turn out to be of much help in her attempt to play the opposite sex.
"His personality is very different, so I didn't learn much from him," she says.
"The assistant director actually gave me advice.
Every day he would say, `Nope, that's wrong,' and he would help me turn it around."
Working with "Papa" Chow, as she calls her co-star/director, was "fun", but he had very high expectations, she says.
"If you didn't do it right, you would do it over and over and over again. So, sometimes, that wasn't that much fun. But, overall, he had a sense of humour."
Her most difficult challenge was a crying sequence near the film's end.
"That was shot at night and I couldn't get the tears out," she says.
"I was really exhausted."
But she knew Chow needed to complete the scene and, finally, she says, the tears began to flow.
She was thrilled when she saw the finished movie.
"It was something I never imagined," she says.
"I always kind of envied those big stars. And almost overnight there I am on the screen. And CJ7 was so cute. He was like he was alive."
Jiao says she might like to try to stick with acting, but she has a more pressing goal: to grow out her hair.
After cutting it for the role and then keeping it short for the promotional tour - 18 months all told - she wants nothing more than to feel a little more feminine.
"I am looking forward to this being over and I can grow my hair long again."
See it: CJ7 screens at Rialto July 30 and 31 as part of the film festival.
