Tricia Helfer and James Callis, <EM>Battlestar Galactica</EM> Tricia Helfer and James Callis, Battlestar Galactica

Acting on Sci Fi Channel's Battlestar Galactica (Fridays at 9 pm/ET) can be torture. Case in point: Fan favorite James Callis is lying in a beautiful, zen-like chamber on the show's soundstage in Vancouver, but the visual serenity of the locale is repeatedly shattered by his head-splitting screams.

This week's episode finds Callis' character, Gaius Baltar, held prisoner by the Cylons, who suspect he has information about a virus that could kill them. When a full-body electroshock — administered by the ruthless Cylon ringleader D'Anna (Lucy Lawless) — doesn't elicit the desired confession, she chooses a wicked-looking item that pierces the eardrum. His screaming begins anew.

After three-plus hours of this sadism, lunch is called, and Callis — shaken, spent and seriously hoarse — retreats to his dressing room. Lawless nonchalantly heads to the chow line. "I love this role, but I could only play that scene by being completely and utterly detached," says the actress, known worldwide as the warmhearted warrior Xena. "D'Anna is Dr. Mengele. You can only do such terrible things if you're fully disconnected from people's pain and humanity."

Even D'Anna has a soft spot, however. "Her humanity will start to grow as the season progresses," Lawless promises. And (Spoiler alert) she adds that her character "will develop quite a little ménage à trois" with Baltar and the bombshell Cylon Caprica Six (Tricia Helfer).

But for now these babes mean business: Later this same day, there's a scene in which D'Anna and Caprica grill Baltar in a more civil manner — except that he's buck naked on a chaise lounge. Cracks Callis, "I don't know what's more torturous, being tortured or being the only naked person in front of a crew of people who are doing everything possible to avert their eyes."

The show's mix of steaminess and brutality is just part of Galactica's wild appeal. The outer-space soap opera — about a duel for survival between the cybertronic Cylons and the human race that created them — is packed with in-your-face politics, mind-bending spirituality and such dicey behavior among the heroes that it's hard to know who the good guys are.

In this same episode, Mary McDonnell's character, the humans' president, Laura Roslin, will turn pro-genocide and decide to use the aforementioned virus to end the Cylon race, even though she owes her life to them. (Her cancer miraculously vanished last season, thanks to Cylon stem cells.)

"Playing this part blows my progressive liberal ideas to smithereens," notes McDonnell, a two-time Oscar nominee. "I'm always balking at things they have Laura do, like how she loves throwing Cylons out the air lock. But then I calm down and see her point of view: The human race is at stake here. I love how this show puts us in other people's shoes."

But it's hell on the nerves. Galactica execs are known for deep-sixing key characters when the fans — and the stars — least expect it. "We have to keep killing people to keep the audience glued — it's that whole sucky thing that Lost started," says Katee Sackhoff, who plays the tough, boozy fighter pilot Starbuck. "Each time we get a script we're like, 'One of us is going, man!'"

And none of the humans can be sure they're really human, since we know there are five more Cylon models yet to be revealed. "It's really quite crazy-making," Callis says. "I asked the producers, 'There's no earthly way Baltar could be a secret Cylon, right?' But I could not get a definitive no."

That's the kind of torture we love!

Sci-fi fans, pick up the Nov. 13 issue of TV Guide for answers to your burning questions about ABC's Lost!

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