By Emily Mitchell/Reported by Wendy Cole

Being on the streets is no joke to Robin Williams. A co-organizer of Comic Relief, the charity laugh-a-thon that aids the homeless, he has joined the ranks of the destitute. It's not for real, but for reel: in a new film, The Fisher King, he's a history professor who lands on Manhattan's Skid Row. During one scene, rats were scurrying around, and, says Williams, "they weren't Hollywood stunt rats. They were real ones who say, `I just ate a cat. Now I want to finish off a dog.'" In New York, even rats have attitude.