The so’o mask, or sokomutu in Swahili (and sometimes referred to as mwisi gwa so’o, suku muntu or ibombo ya soho in some sources), belongs to the Hemba people of the Democratic Republic of the Congo. So’o means "chimpanzee-human", and is intended to personify death. The Hemba regard the chimpanzee to be a predatory animal and a symbol of aggression. Some say the so’o covets human women and humans’ opposable thumbs, and if the opportunity arises, it will seize it. The mask, which bears an aggressively toothy grin, represents a frightening, unnatural creature. Sometimes, the mask might embody a deceased ancestor and bear his name. In either case, the so’o is fickle in its moods and it can be either helpful or hurtful to the living.
When used in a funerary context, the so’o mask represents death. At funerals, the mask appears at the end of the series of funeral rites to signify the conclusion of the mourning period. The mask is used in a performance that helps people transition from a state of grief back into their daily routines.
In Hemba funerary festivals such as the ubuzha malslo, the so’o is used in two phases. The "wild" phase is the first phase, which includes a chase. The so’o enthusiastically chases everyone to frighten them, especially young children and pregnant women, away from the village. Everyone who runs outdoors is considered safe; if one runs into a house and is followed by the so’o, they must undergo initiation into the so’o secret society. For this reason, older people, particularly senior men rarely run. During the second stage, the so’o is performed, accompanied by a drum and songs. This signifies the return of spatial order; no one runs any longer. In its performance, the so’o acts as a clown or trickster, playfully mocking the normal order of society.
While the so’o represents death, it is also linked to fecundity and fertility. Ruined crops can be interpreted as a sign that one must be initiated into the so’o society.