The bacterium that causes tetanus is Clostridium tetani, which is an anaerobic bacterium. If the wound is deep and enclosed in an environment lacking oxygen, it creates a suitable environment for the growth and reproduction of Clostridium tetani. Its incubation period is generally around one week. Early symptoms may include general fatigue, localized muscle tension, and uncontrollable spasms. The first muscles affected are usually the facial chewing muscles, and it can then progress to intense, spasmodic contractions of muscles throughout the body, and even cause fractures. Mild stimuli such as light, sound, or drinking water can trigger and worsen these symptoms, somewhat similar to rabies. However, a characteristic feature of tetanus is that the patient remains mentally clear. Most patients may die from respiratory spasms leading to asphyxiation, heart failure, or lung infections.