Eliza Dushku Eliza Dushku

"Comedy is definitely a huge part of who I am," insists Eliza Dushku, best known for playing tortured vampire killer Faith on Buffy the Vampire Slayer and the tragic fembot Echo on Dollhouse. "I know everyone says that, but I am freakin' hilarious."

She'll get to show off her comedic talents on tonight's episode of The Big Bang Theory (8/7c, CBS). Dushku guests as a deadpan FBI agent dispatched by the Feds so that aerospace engineer/delusional ladies' man Howard Wolowitz (Simon Helberg) can get high-security clearance. Like her guarded character, Dushku can't divulge any details, but she will say this: "[Howard's friends] are definitely telling me things they shouldn't."

In anticipation of the role, Dushku did a little unscientific market research. "I use Twitter like throwing spaghetti at the wall," she says. "When I talk about the show, people — and I do have a pretty hefty number of nerd followers — go nuts."

Subscribe to TV Guide Magazine now!