It's busy down there: a gut bacterium splits into two, becoming two new cells. Centre For Infections/Science Photo Library/Corbis hide caption

itoggle caption Centre For Infections/Science Photo Library/Corbis

Bad bug: The bacterium Clostridium difficile kills 14,000 people in the United States each year. Janice Carr/CDC/dapd hide caption

itoggle caption Janice Carr/CDC/dapd

Sucking may be one of the most beneficial ways to clean a baby's dirty pacifier, a study found iStockphoto.com hide caption

itoggle caption iStockphoto.com