"It's hard to have a sex scene, period. It doesn't matter if it's a friend, a male, a female," News.com.au quoted her as saying. "You're with 100-something crew members, lighting you, repositioning you, there's no comfort whatsoever," she said.
Last month, Kunis slammed reports that the pair had downed tequila together before their risque shoot. "I don't think we could have done that scene if we were intoxicated," she told People at the time.
Both Kunis and Portman have discussed their gruelling training regimes for the film that saw them lose drastic amounts of weight. Five to eight hours a day of cross-training and swimming for a year saw both the petite stars shed 10kg each off their slight frames.