Hayden Panettiere

By Michelle Tan/Los Angeles

UPDATED 04/16/2007 at 01:00 AM EDT • Originally published 04/16/2007 at 01:00 AM EDT

Warning! If you spot Hayden Panettiere strolling in L.A. looking bruised or beaten, do not call 911. During lunch breaks while filming Heroes on location, Panettiere—who has survived everything from a fire to an autopsy as the show's self-healing cheerleader Claire Bennet—often wanders around town with her costars "and we're all wearing blood," she says. "People are like, 'What the hell?' It's Halloween for us every day!"

For that autopsy scene, Panettiere, 17, was splayed out with her organs exposed and "she was singing her lungs out between takes," says Heroes creator Tim Kring. "She keeps things light. If we had a blooper reel, it'd be almost all Hayden."

Since becoming the focal point of Heroes' "save the cheerleader, save the world" plot line, Panettiere has also started filming the drama Fireflies in the Garden with Julia Roberts and is gearing up to promote her debut pop album this fall. "With singing I get to be myself," she says.

And later this spring, she'll celebrate another milestone—high school graduation. "Thank God!" says the Nyack, N.Y., native. "School was difficult; when you come and go, you miss out on a lot. Cliques are formed and you're just lingering."

In L.A. Panettiere has found a BFF in Bruce Willis and Demi Moore's daughter Rumer ("I stole my pink belly-button ring from Rumer," she admits) and a boyfriend in Laguna Beach's Stephen Colletti, 21, whom she's been dating for over a year. The two stay so low-key (usually dinner and a movie) that the actress feels guilty about not giving gossipmongers more to work with. "I had paparazzi on my street for a while," says Panettiere. "I think I bored them to tears. I'm no fun to watch."