fleas

The mystery: How did bubonic plague spread so rapidly? Could rat fleas have done it all? A new study points the finger at lice as possible accomplices.

Doctors have long thought that cat-scratch fever is no big deal, but an analysis finds that more people are getting sicker from it. Small children are especially at risk, as are people in the South.

It's a bloodsucking creature. But it's not a vampire. Or a vampire bat. Here's a look at the eight deadliest animals on earth (and a costume primer).