Toxoplasma gondii is one of the fascinating little parasitic creatures capable of changing the natural behavoir of its infected host. It needs to live in a cat in order to reproduce, but the rest of its life cycle can be spent in just about any warm-blooded animal. When it makes its way into a rat or mouse, for example, it has the peculiar ability to render the rodent unafraid of cats and even drawn to their scent. This powerful evolutionary trait increases the T. gondii's chances of reproduction—a mouse hanging around with cats is obviously likely to be eaten. In recent years, T. gondii has been mysteriously appearing in sea mammals. Scientists have been at a loss to explain the mechanism of infection, considering dolphins and seals aren't usually cavorting with cats.