Chris Evans' Costar Loved Groping His "Man Boob" in Captain America

Actress Hayley Atwell was extremely hands-on for her role in Captain America: The First Avenger (in theaters Friday).

In one scene, the 29-year-old actress gropes costar Chris Evans' chest after he undergoes a radical science experiment that transforms him into a beefed up action hero.

PHOTOS: Hollywood's buff boys

"That was an instinctive moment. I literally couldn't help myself, because I hadn't seen him with his top off until that moment," Atwell tells Pop Sugar. "I mean, go for the man boob! And [the director] loved it. He was like, 'Do that again!' So we ended up doing lots of takes just to see how far we could go, and then got a little bit over the top."

PHOTOS: Stars as super heroes

How over the top, exactly? "There was the touching of the nipple, and it became like a Saturday Night Live sketch. It was kind of ridiculous. Really corny."

That wasn't the only time Evans, 30, surprised Atwell (who earned a Golden Globe nomination last year for her role in the TV miniseries Pillars of the Earth).

PHOTOS: This summer's hottest movies

"He's a really good musician, a good singer, and a really good dancer, too," Atwell says. "So I think I was surprised at that, because a lot of the things I'd seen pictured him as a kind of goofy jock. Kind of a strong, masculine guy. And there's a lot more to Chris that will be revealed, I'm sure, in his career. He's a very, very talented young man."