On a shallow reef in the Florida Keys, a young Caribbean spiny lobster returns from a night of foraging for tasty mollusks and enters its narrow den. Lobsters usually share these rocky crevices, and tonight a new one has wandered in. Something about the newcomer is not right, though. Chemicals in its urine smell different. These substances are produced when a lobster is infected with a contagious virus called Panulirus argus virus 1, and the healthy returning lobster seems alarmed. As hard as it is to find a den like this one, protected from predators, the young animal backs out, into open waters and away from the deadly virus.