Hayden Panettiere’s On-Set Smooch Session

We're used to seeing her getting cozy with her boyfriend/Heroes co-star Milo Ventimiglia. But yesterday (September 14), Hayden Panettiere was spotted locking lips with a different dude.

But it wasn't an act of cheating - the Save the Whales Again activist was on the set of her current movie "I Love You Beth Cooper" filming scenes with her co-star Paul Rust.

And Miss Panettiere looked totally hot in a sexy strapless merlot-colored dress as she spent the day on the Los Angeles, California set.

"I Love You Beth Cooper" is about a nerdy valedictorian who proclaims his love for the hottest, most popular girl in school during his graduation speech. It hits theaters March 27th, 2009.

Enjoy the pictures of Hayden Panettiere (and Paul Rust) on the set of "I Love You, Beth Cooper" (September 14).