Was that Brad Pitt, or just a guy with a sock on his head? Only Taraji P. Henson knows for sure.

In

The Curious Case of Benjamin Button

(opening Christmas Day), Henson is Queenie, a New Orleans retirement-home caretaker who, one night in 1918, discovers what appears to be an abandoned infant on her back porch. Queenie takes this tiny creature indoors - its name is Benjamin Button - unwraps the blanket, and beholds a gnarled old visage on a newborn's frame. As the years proceed, Benjamin Button - adopted and raised by the African American Queenie - gets bigger, naturally. But he also gets younger and stronger, most unnaturally.

Indeed, in

The Curious Case of Benjamin Button

- inspired by a bit of F. Scott Fitzgerald whimsy, a short story about a man born old who ages backward - the title character journeys from the end of World War I into the 21st century. For many of those decades, Henson's character is there to nurture and advise, looking on proud and wise.

But that doesn't mean the actress was always in the same room with Pitt.

"The first time I worked with Brad

as

Brad, Brad's face on Brad's body, was when Benjamin comes back from the [Second World] War," says Henson, whose performance in the David Fincher-directed release has some people talking about a supporting-actress Oscar nomination for her.

"But prior to that they hired actors of various sizes - three different actors - to portray him younger," she explains. "Well,

older

, actually."

These actors were of small stature, starting with a most diminutive fellow. And they would wear what Henson describes as "something like a blue sock" over their heads, with a hole for the face to poke through. In post-production, the digitally rendered likeness of a geriatric Pitt, replete with a gamut of highly nuanced expressions, would be "painted" over the actors' faces.

"There would be a bunch of X's and O's on the blue cap," Henson says of the green-screen process, "so that they can later go in and digitalize Brad's face on it. And not just Brad's face. They had to put hair on, and you could see his pupils dilate. It's incredible what they did!"

And it's incredible what Henson - who goes through the movie acquiring more traditional old-age makeup and prosthetics - does with her role, exuding warmth, humor and grace.

Henson, 38, in Philadelphia recently to talk up the film, was stationed in a hotel suite alongside an easel with a poster of

The Curious Case of Benjamin Button

, and its star, the Bradster, on it.

"Brad?!" she exclaims, rolling her eyes over at the poster. "Loving him! The best man ever!"

Henson, who hails originally from Washington, and now lives in Los Angeles, couldn't help but wax ecstatic about her costar.

"Of course he's talented, we know that," she says. "But I just so enjoyed getting to know him as a person, as a father, as a great humanitarian. . . . He's just so real, and so down to earth. And as an artist so giving, and so there for you - and he doesn't have to be. I've heard horror stories about stars of that stature."

Henson's first name is the Swahili word for hope - the P. is for Penda, which means love. A graduate of the drama program at Howard University, she's been working in TV and film since 1997. She credits John Singleton with her big break in movies, in the director's 2001 L.A. family drama

Baby Boy

.

It was Henson's performance in 2005's

Hustle & Flow

- as Shug, the pregnant prostitute opposite Terrence Howard's rap-sodizing pimp - that brought her to the attention of

Benjamin Button's

casting director, Laray Mayfield.

"I didn't think I had a chance at getting the role because it's a big studio film with big names attached, and I just figured they're going to go for a big name," Henson says, about going for her audition. "But unbeknownst to me, Laray had seen - two years prior to

Ben Button

even being green-lit - she had seen

Hustle & Flow

. She was in the theater watching my performance and she called Fincher and she said, 'I found Queenie.' "

Henson, a single mom with a 14-year-old son, has three titles coming in the new year.

Not Easily Broken

, opening Jan. 9, is a drama with Morris Chestnut in which a marriage is put to the test. ("It's about what it takes to make a relationship work," she says.)

Hurricane Season

, with Forest Whitaker, is a true-life sports drama about a Louisiana high school basketball coach who leads his team to the championships in the aftermath of Katrina. Its release date has not been set.

And in the indie

Once Fallen

, from writer-director Ash Adams, Henson plays the girlfriend of the son of an Aryan Nation leader. Ed Harris and Brian Presley costar. "I've never had a white love interest, so I was excited about that," Henson says of the racially charged drama. "I'm open to whatever, I just love the craft of acting."

Contact movie critic Steven Rea at 215-854-5629 or srea@phillynews.com. Read his blog, "On Movies Online," at http://go.philly.com/onmovies.