Russian-born actress Mila Kunis admitted on Ryan Seacrest’s radio show that she used a butt double for the more graphic scenes in her new flick, Friends with Benefits.

With that being said, Kunis didn’t want just anyone’s butt to stand in for her own, so she, along with director Will Gluck, the film’s casting director, and the makeup artist, held a casting call for Kunis’ butt double — and watched a parade of women moon them so that they could make the best decision!

“These young ladies came in and they were in a casting room and I was there with the director and the casting director… and these lovely women had to show us their derrieres and we chose the one that most resembled my body the most,” explained the 27-year-old Black Swan star. “Besides,” she went on, “I showed side-boob, and I figured I can’t just give away everything all at once. I have to let out little pieces here and there.”

While Kunis opted to keep her buns private, her costar Justin Timberlake did not. Though Timberlake joked that he’s tried to “get into the editing room to cut down on my ass time,” he seemed at peace with the world gazing at his bare bum.

“I only did it because I’m young now, and everything’s where it’s supposed to be,” the 30-year-old singer/actor told Vanity Fair. “I figured this is the time, before gravity gets the best of me.”

Kunis and her substitute derriere went on display in theaters across the country on July 22nd.

Watch Mila and Justin talk about “the awkwardness of being nude in front of the camera” on the Ellen Degeneres Show.