When Kristen Stewart and Dakota Fanning signed up for "The Runaways," a biopic that would have them playing '70s punk rockers Cherie Currie and Joan Jett, a lot of people said it would be a cinch -- just put on the leather pants, check the hair and roll the cameras. But when MTV caught up with the BFFs recently to discuss the new flick, we discovered that the two hardworking stars were so determined to get things right that they even utilized some sleight of hand.

In a split-second, blink-and-you'll-miss-it-shot from the movie, the teenage rockers sit down to sign their first big recording contracts. If you look closely, you'll see that both Stewart and Fanning sign with their left hands. So, we had to ask a geeky but enlightening question: Are they really left-handed?

"They're left-handed," Fanning explained. "I'm right-handed."

"Uh-huh, they're left-handed," KStew agreed. "And I'm right-handed."

When it came time to shoot the movie, why did the two teen actresses care so intensely about a tiny detail that no one -- OK, well maybe just us -- would ever notice?

"We knew we were going to have a scene where we were going to have to sign something, so you need to ask [the real-life people you're portraying]," Fanning explained, giving us just a sample of the

tt-preps-for-runaways-biopic/">behind-the-scenes minutiae the actresses used while studying Currie and Jett.

Stewart agreed that although the two shots are literally a split-second each, the two young Hollywood stars take their acting jobs very seriously.

"Joan [has a distinctive writing style]; I had a couple other little writing bits [I noticed] because I've seen her write," Stewart added, saying that the mimicry went so far that fans might also notice the way she hooks her left arm around the pen. "Curled over," added Dakota, demonstrating the move.

"Yeah, exactly like this," Stewart agreed, clearly enthused that people would pick up on such tiny details of her performance. "It's almost like she's hiding [the pen]."

It's only one of countless decisions KStew and Dakota made while capturing the real-life rockers -- from how to stand, to how to sing, to the way they spoke to each other. Both were insistent that they spend a great deal of time with their real-life counterparts, and insisted that the research paid off.

"[Joan Jett] does write a little weird. And that's why it was so great having her around, not just [for little stuff like that], but for the emotional connection -- to capture an essence, and they are such vivid people," Stewart said of her method. "It was great to have her there."

Check out everything we've got on "The Runaways."

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