It takes a lot to make Angelina Jolie blush.

This is the woman, after all, who wore nothing but her birthday suit in Gia and romped naked in a bathtub with Antonio Banderas for Original Sin.

But while watching Beowulf, the actress admits to turning five shades of crimson.

“I got a little shy,” says Jolie. “There were certain moments where I actually called home, just to explain that the fun movie that I had done that was digital animation was, in fact, a little different than we expected. I was really surprised that I felt that exposed.”

Jolie’s character – a sexy, high heels-wearing swamp thing – is one of the biggest surprises of Beowulf, Robert Zemeckis’ adaptation of the ancient poem.

The plot, as anyone who’s suffered through freshman English knows, revolves around a Scandinavian warrior named Beowulf (Ray Winstone) who saves King Hrothgar’s (Anthony Hopkins) people from the ruthless monster Grendel (Crispin Glover) and his equally scary and slithery mom (Jolie).

Budgeted at $150 million, the PG-13-rated Beowulf uses motion-capture technology to transform live action into digital animation. Zemeckis (Forrest Gump), working from a screenplay by Roger Avary (Pulp Fiction) and Neil Gaiman (Stardust), refined a technique he’d used previously in The Polar Express. (Director Peter Jackson also employed motion-capture technology to bring Gollum to life in the Lord of the Rings movies.)

Beowulf bears the distinction of being the largest 3-D release of any film in history.

For Jolie, the most eye-popping part of watching Beowulf was seeing herself as a gold-plated woman-reptile, with high-heeled cloven feet and an appendage-like braid of hair.

“I really wasn’t expecting my character to look so real,” says Jolie. “ I didn’t expect [myself] to come out as much. But it’s fun. And I do love my tail.”

As far as Zemeckis is concerned, there was only one choice for the role of Beowulf’s hot and hellacious mama.

“Grendel’s mother is a demon and a seductress to the nth degree and nobody can do that kind of sultry character as well as Angelina Jolie,” says the filmmaker. “When she stepped on the set and became that character, it was a powerful thing to watch. She was just magnetic and she hypnotized everyone on the set.”

Since beginning a relationship with Brad Pitt in 2005, Jolie’s film career has been a bit overshadowed by her personal life. But in addition to being a globe-trotting activist and mother to four kids – Maddox, 6, Pax, 4, Zahara, 2 and Shiloh, 17 months – Jolie has continued to turn out about two movies a year.

This summer, she starred as reporter Mariane Pearl in A Mighty Heart, a film about the kidnapping and execution of Daniel Pearl by Islamic extremists. The movie received positive reviews but failed to make a dent at the box-office.

“It’s not a disappointment at all to me,” says the actress. “It’s a film that I feel strongly about, and Mariane – and Danny’s parents – feel strongly about. The people who see it appreciate it. It was only [a disappointment] in box-office dollars, and that has little to do with art.”

Still in the works from Jolie: Wanted (2008), a thriller co-starring James McAvoy and Morgan Freeman; Kung Fu Panda, an animated flick co-starring Jack Black; and Clint Eastwood’s The Changeling (2008), a drama about a mother whose kidnapped son returns home transformed.

“I have one more month on The Changeling and then I’m not working for a while,” says Jolie, 32.

Asked about how she manages to juggle work and kids, the actress says, “Brad and I take turns working. It’s not that hard to balance it all.”

Still, Jolie admits that one of the draws of Beowulf was the chance to shoot a movie while three months pregnant with Shiloh. Even though Jolie is a major component of the adventure, she estimates she spent less than week on the set.

Like all of the other actors, Jolie donned a lyrca wetsuit suit decorated with dozens of digital sensors before slinking and slithering around the studio to bring her character to life. Her “captured” performance was then input into computers at Sony Pictures Imageworks.

“I never call Beowulf an animated movie because we were all physically doing these things you see in the movie,” says Jolie. “Every single gesture is ours, everything is acted out, even the way our eyeballs move.”

Jolie says she had no idea what to expect from the film, which marks her third venture into animation after Shark Tale and Sky Captain and the World of Tomorrow. The main reason Jolie agreed to Beowulf was for the opportunity to work with Zemeckis.

“I would have said yes to pretty much anything for Bob Zemeckis,” she explains. “He told me I was going to play a lizard and showed me drawings of gold-painted women. I have kids and I thought, ‘That’s great. It’ll be fun for them to see me as this bizarre, crazy reptilian creature.’ ”

Initially, Jolie wasn’t certain she’d enjoy the motion-capture process.

“I thought, ‘Oh this is going to be so weird, all of us actors with these dots on our faces, in these wetsuit-type costumes, with no props or sets,’ ” she says. “But what it really does is strip everything down to the essentials of performing, especially in the scenes between Crispin and me. They were just pure amazing emotion.”

Jolie maintains she had no trouble sympathizing with the movie’s monster mama. “When you mention Grendel’s mother, you find that everyone has an opinion about her,” notes the actress. “I think she’s lovely and everybody else thinks she’s a bit off.

“Yes, she’s a monster, but she’s also a mom and that’s the essence behind everything she does. Grendel is like a full-grown man but there’s something vulnerable and childlike about him. I thought about her as a mother. If someone hurts your son, you would go to the ends of the earth to avenge him. So, I approached it that way.”

Jolie remembers reading Beowulf in high school but it didn’t make a big impression on her.

“I think I read it half asleep,” she says with a laugh. Her tastes ran more to Treasure Island and Winston Churchill biographies. “I loved stories about Churchill’s early life, and his adventures,” she explains. “I’ve always been fascinated by history.”

Jolie is also fascinated by a handful of humanitarian issues, from stamping out AIDS in Africa to building orphanages in Maddox’s native Cambodia.

“Brad and I both have a lot more work to do in New Orleans,” she says of rebuilding projects the couple has initiated in the region. “We also want to continue to work with an education program we started [in Cambodia]. There are refugees that need our help. There are many things to do.”