the three worms; the three corpses
In Taoist belief, three supernatural worms or spirits that reside in the human body and ascend to heaven on the night of Kōshin (庚申) to report the person's misdeeds. Often referenced in the context of Kōshin-machi (庚申待) all-night vigils.
See also: 庚申待
During Kōshin-machi, people stay awake all night to prevent the three worms from ascending to heaven and reporting their wrongdoings.