Naomi Watts has appeared opposite some of the greatest stars in cinema — Sean Penn, Viggo Mortensen, Leonardo DiCaprio, even King Kong. But none of those leading men prepared her for Bing, the 145-pound Great Dane she co-stars with in “The Friend,” a drama about heartbreak, art and a very big dog that screens at this year’s Toronto Film Festival.

And getting comfortable with Bing was a six-week process that involved more than handing out a few treats. Bill Berloni, the veteran animal trainer whose job it was to prepare Bing for his close-up, insisted on having Watts meet two times a day for 20 minutes each with the dog, so she could learn how to control the lumbering giant on the streets of New York City, where “The Friend” was shot.

“Initially, I thought, is this necessary?” Watts admits. “I’m an animal lover. I’m not put off by a little fur and slobber.