A len dong ceremony is a procession of persons through one body. The medium, the ba dong or ong dong, sits before the altar draped in a red veil; the chau van musicians strike up the invocation of a spirit of the celestial court; and when the spirit descends, the veil is cast off and the medium rises transformed, robed by two assistants in the spirit's colours, red for one realm, green for the mountains and forests, white for the waters. The order of incarnations follows the pantheon's hierarchy under the Mother Goddesses of the Three Realms: the great mandarins, dignified and formal; the ladies; the princes, who may dance with sabres or flaming ropes; the princesses, graceful with fans and flowers; and the young princes and the child spirits, playful, teasing, fond of cigarettes and dance. Each spirit works its character: it dances, receives offerings, listens to petitions, and distributes loc, blessed gifts, money, fruit, cakes, flung or handed to the devotees, whose scramble for them is part of the joy; the atmosphere is closer to festival than to solemnity, and the tradition itself says the spirits come to play.
Beneath the spectacle the rite does earnest work. People come to len dong with illness, bad fortune and grief; many mediums enter the practice through affliction interpreted as the call of the spirits, and the ceremony resolves the calling into vocation, a pattern anthropologists of the tradition, Philip Taylor and others, have documented in detail among the market women who form much of its base.