Sex Siren Status?

So my friend D was updating me on recent celebrity gossip (soooorrrry I've been too busy writing a novel to read TMZ in a while, ok?) and we got to discussing the Sienna Miller / Balthazar Getty affair.

Now, I'm not judging, and the last thing I'm going to do is devote a blog post to what a sleezeball Getty is and how Sienna Miller is a hypocrite for ruining a relationship when her own was destroyed by a nanny. No, no, what I am riled up about is how Sienna Miller always manages to bag all these hotties. Jude Law, Orlando Bloom, Leo DiCaprio, Hayden Christensen, Josh Hartnett, and now Balthazar Getty. How is that fair?!?!

Sienna is a pretty girl, no one's denying that. She has a great body, blonde hair, and style sense that any girl would kill for. But that does not translate to "make hot men fall at their knees." So what's that je ne sais quoi that she's got?

D and I decided that she comes across as a sex siren. And that's the extra something that sets her apart from the rest of the pretty blondes out there. Now, how does one go about being a sex siren?

I wandered into Barnes and Noble and asked if they had any books on how to be a sex siren, "Sex Sirens for Dummies," if you will, and they just looked at me blankly. So it looks like it's going to take a little more work for me to crack that mystery. How does one go from just being the girl-next-door type to the sex-siren type?