Rapper-turned-actor Will Smith cheered up the crew of his new movie I AM LEGEND by giving an impromptu musical performance on set. The 39-year-old was fed up with the freezing weather conditions while filming in New York so he launched into a rendition of his 1991 hit Summertime - to keep production staff's spirits up. He says, "This was a major six-night shoot involving a crew of 250, more than a thousand extras and many more people who turned up to watch. "One night it was freezing cold so I grabbed the mic and started rapping Summertime. It wasn't planned. A microphone to a rapper is like a magnet. I can't leave it alone."