'The Girl With the Dragon Tattoo' star Rooney Mara: Getting my nipple pierced was like wearing a 'costume'

Rooney Mara is a dedicated actress.

The dainty star of "The Girl With the Dragon Tattoo," 25, toughened up for her role in the epic thriller - and went to extreme lengths to get into character, including a small, but painful, physical transformation: a nipple piercing.

"I'm naked quite a lot in the movie, and I thought, she has it in the book, and she should have it (in the movie)," she told the January issue of Allure.

Mara plays the role of computer-hacker Lisbeth Sander, who is oft naked and always edgy. The actress explained that in order to fully embody the character, she knew she had to go beyond just wearing the right clothes.

"Because of all the tattoos and makeup and the piercings, and the physical transformations my body has to go through, it would always feel sort of like I was in costume, even if I was naked.

"It just felt like a good one to get - a necessary one to get."

And stripping down in front of the camera soon became the norm for "The Social Network" actress, who wanted to stay as true to the book as possible.

"Nudity is such a huge part of the character in the book, so I never thought twice about it," she said. "There was no time for hesitation. I didn't have time to second-guess anything or be scared; I just showed up and was comfortable."

For the film, Mara also had to get piercings in her ears, on her lip and in her nose, as well as hack off a substantial portion of her hair and bleach her eyebrows. Surprisingly, her ears turned out to be the most sensitive part of her body.

"I didn't even have pierced ears," the actress said. "They put four holes in each ear, and, weirdly, that hurt the most."

Mara's tough-girl character is out of line with her usual "girlie, frilly" wardrobe, but likely more in-synch with her family's famous football roots.

The actress' great-grandfathers were New York Giants founder Tim Mara and Pittsburgh Steelers founder Art Rooney, Sr., and dad Timothy Christopher Mara is the Vice President of Player Evaluation for the Giants, while her uncle, John Mara, is the current co-owner.

"I didn't love football growing up, and I'm not obsessed with it," she said. "My whole family is really into it. I'm not. But I do really like it, and of course I appreciate it because of my family - it's a huge part of my heritage."

"The Girl With the Dragon Tattoo" is set to be released on Dec. 21.