Three Corpses

The sanshi 三尸 "Three Corpses" or sanchong 三蟲 "Three Worms" are a Daoist physiological belief that demonic creatures live inside the human body, and they seek to hasten the death of their host. These three supernatural parasites allegedly enter the person at birth, and reside in the three dantian "energy centers", respectively located within the head, chest, and abdomen. After their human host dies, they are freed from the body and become malevolent ghosts.

The pernicious Three Corpses/Worms work to harm their host's health and fate by initiating sicknesses, inviting other disease-causing agents into the body, and reporting their host's transgressions to the gods. The Three Corpses are supposed to keep records of their host's misdeeds, ascend to tian "heaven" bimonthly on the night of Chinese sexagenary gengshen 庚申 "57th of the 60-day cycle" while the host is sleeping, and file reports to the Siming 司命 "Director of Destinies" who deducts a certain number of days from the person's life for each misdeed. One way of avoiding this bureaucratic snitching is to stay awake for the entire gengshen day and night, thus preventing the Three Corpses from leaving one's body (a belief later assimilated into the Japanese Kōshin 庚申 tradition).

For a Daoist adept to achieve the longevity of a xian "transcendent; immortal", it was necessary to expel the Three Corpses from the body. Since these evil spirits feed upon decaying matter produced by grains being digested in the intestines, the practice of bigu "abstinence from grains and cereals" is the first step towards expelling them. Bigu alone will not eliminate the Three Corpses, but weakens them to the point where they can be killed with waidan alchemical drugs such as cinnabar, and ultimately eliminated through neidan meditation techniques.