Your cat is a killer. And we're not just talking about the hit to your soul when Fluffy stares right past you despite your sweetest cooing. Cats, no matter how adorable, are predators. They stalk, they pounce -- and then they snap the neck of whatever little flying or skittering thing they've just caught. Most of us view this as a good thing. We're all better off with fewer rodents around, and if some pretty little birds get caught up in the killing spree, we can live with that. Biologists, it seems, aren't so sure. Domestic cats aren't a natural...