The bacterium that causes tetanus is called Clostridium tetani. The bacterium can survive in a dormant state in soil and animal feces. It's essentially shut down until it discovers a place to thrive. When the dormant bacteria enter a wound — a condition good for growth — the cells are "awakened." As they are growing and dividing, they release a toxin called tetanospasmin. The toxin impairs the nerves in the body that control muscles.