Tetanus is a specific infection caused by the bacterium Clostridium tetani entering the human body through wounds in the skin and mucous membranes, proliferating massively in an anaerobic environment, and producing toxins. It is primarily characterized clinically by lockjaw and episodic or sustained muscle spasms. The incubation period of tetanus is usually seven to eight days, but it can be as short as twenty-four hours or as long as several months, or even years.