"Clostridium tetani" causes tetanus. Usually, people get tetanus when they get a cut or wound, and "Clostridium tetani" bacteria get into the wound. At first, tetanus causes the muscles in the jaw to spasm (tighten). (Tetanus is often called "lockjaw" because the jaw muscles spasm so badly that the jaw seems "locked.") This can make it difficult to swallow. As tetanus gets worse, other muscles in the body get stiff and spasm.