Mila Kunis and Justin Timberlake Get Their Backs Into It in 'Friends With Benefits'

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Mila Kunis and Justin Timberlake's off-screen antics mimic their on-camera chemistry in 'Friends with Benefits.' ET's Chris Jacobs spoke to the dynamic duo about their backsides stealing so much screen time.

"I don't feel comfortable talking to another man about it," Justin told Chris. Mila pried a response out of him instead, prompting him to describe the experience as "airy" and "breezy." The "shameless" multi-faceted entertainer and entrepreneur added, "I was Mila's stunt butt." Another headline-making derrière belongs to Your Royal Hotness, Pippa Middleton, who Justin calls "smokin'."

The two megastars gave Patricia Clarkson quite an eyeful on her first day of filming. "I walk[ed] in on two of the hottest stars in Hollywood naked! It was a very fun way to start shooting; to see them in all their glory."

In a successful 20 year relationship with her husband, Jenna Elfman begs to differ from the theme of the movie. "There are booty calls and there are relationships," she compares. She doesn't see room for gray area in the middle. Though Justin jokes about his "[Bleep] in a Box," on "Saturday Night Live," he advises people to "be safe" in their rendezvous.

Some cast members have crossed paths before. In a "SNL" skit, Patricia portrayed Justin's mom, though she plays the role of Mila's troublesome mother in this film. As a young child, Mila previously worked with Jenna in 'Krippendorf's Tribe.'

'Friends with Benefits' brings laughter to theaters on July 22.