They also chat about their images (prude vs. sexy) and politics (Hillary vs. Obama )

Natalie Portman and Scarlett Johansson, who star as sisters in the upcoming film The Other Boleyn Girl, vamp it up for the new cover of W magazine – and they set the record straight on everything from monogamy to politics.

On relationships, Johansson, 23, gets her chance to explain an old comment in which she said she didn’t believe humans are meant to be monogamous.

“I’ve been battered for saying that I don’t believe humans are monogamous by nature. The response was, like, ‘What a ho-bag!'” she says in the mag’s March issue (read the whole story here). “I didn’t mean that I don’t practice monogamy in my own life – of course I do! I’m not going to be in some tarty relationship. But I stick by what I said. I remember another time, I said I get tested for AIDS twice a year, and again that got spun as me being promiscuous. But I was single at the time, and I think it’s important to do that!”

And Portman, 26, has her costar’s back. “I’m into monogamy. But I’m not really into marriage right now,” she says. “I sort of hate the legal aspect of it. What does the state have to do with it? Why are they making rules that say my lover can stay in the United States if they’re foreign or share my health care benefits because I’m straight – but if you’re gay, you can’t have that?”

Good Girl vs. ‘Harlot!’

Portman also talks about the public perceptions of their respective personalities. She tells Johansson: “I get branded a lot as a good girl. I’m, like, the prude, and you’re more sexy, more like…”

“A harlot!” Johansson replies, laughing.

Portman, meanwhile, says she often gets branded as “boring.”

“I don’t think you’re boring,” Johansson adds.

“Thank you,” Portman replies, “I appreciate that.”

Getting Political

The two women also get a chance to talk about the presidential campaign, with Johansson a vocal supporter of Democratic presidential candidate Barack Obama (“I will continue stumping for Obama until he’s elected,” she says) and Portman giving some love to Hillary Clinton (“I met with about 10 representatives … and Hillary was by far the sharpest”).