Rooney Mara and Dragon Tattoo director play the numbers

No brainer: You've been cast as Lisbeth Salander, the savant punk problem-child and hacking whiz of Swedish novelist Stieg Larsson's Millennium Trilogy, so of course you start pouring over the books. Not just The Girl with the Dragon Tattoo, but The Girl Who Played with Fire and The Girl Who Kicked the Hornet's Nest, too.  And Rooney Mara, the actress who brings Lisbeth uncannily to life in the just-released David Fincher-directed thriller, also studied volumes about the victims of sexual abuse. Salander, who allies with a Stockholm journo (Daniel Craig) to solve a decades-old mystery, was herself damaged by sexual abuse – both in her childhood, and in a brutal encounter with a court-appointed guardian that is central to the Dragon Tattoo storyline.

But here's another source Mara says she dove into, to help her understand the complicated character she played: books from the Enneagram Institute, home to an elaborate system of personality profiling by numbers.

"David's really, really into it," Mara reports, on the phone recently, "and he got me really into it, so I read a lot about the Enneagram…. It's this personality typing where there are these nine different types -- nine different categories that people can fall into. So I had him tell me what number every character was [in the film], and I did a lot of reading on that. I sort of became obsessed with it."

Mara reports that Lisbeth Salander is a 5, not surprisingly dubbed "The Investigator." Here's a Type 5 description, from the Enneagram website: Fives are alert, insightful, and curious. They are able to concentrate and focus on developing complex ideas and skills. Independent, innovative, and inventive, they can also become preoccupied with their thoughts and imaginary constructs. They become detached, yet high-strung and intense. They typically have problems with eccentricity, nihilism, and isolation. At their Best: visionary pioneers, often ahead of their time, and able to see the world in an entirely new way.

And what about Mara herself?

"I have a number," she says, laughing. "But I don't want to give it away."