This is one trend we don't get, but hey, celebs are all about it and they're the ones (allegedly) setting the style rules.

Actress Rosario Dawson, who sports a lush, thick mane of glossy dark hair, has shaved half her head -- a look we've also seen on Rihanna and Jenna Jameson, to name only a few. 

As you can see from the photo, Dawson has thinned her mane and sheared off a good portion of it. It's a punk rock look. She was spotted with her new 'do, casually flipped to one side, while on set of her new film 'Finally Famous.' (Yes, that's Chris Rock in the background. He does not, for the record, have a half-shaved head. He's just close-cropped.)

While Dawson is gorgeous and can take a lot of style risks and liberties, we're still baffled about why the stars are doing this. Is there some need to be "punk rock" that truly took off when Miley Cyrus decided that chopping off her hair was the edgy and cool thing to do? (God help us when Miley is the yardstick by which hair trends are measured.)

Regardless, it's just hair and it grows back. We hope.