The main attraction at Berlin zoo these days is a cuddly polar bear cub called Knut. However, there was some controversy about his early life - his mother, Toscana, rejected him, his twin brother died, and animal rights activists suggested the zoo should have allowed him to die rather than care for him. Fortunately for delighted Berliners, he was hand reared by zoo keepers and made his public debut on Friday (auf Deutsch): However, tragedy struck for Berlin Zoo when its now second most popular inhabitant, a panda named Yan Yan, died on Monday. The cause - Knut. Apparently, Yan Yan couldn't take the stress of all those visitors. Cute as Knut is, when he's fully grown he could weigh as much as 600kg and be up to 2m in length... a real killer.