Religious Beliefs. Landtman gives little information about Kiwai religious beliefs, but he notes that their religious beliefs are not systematic. The Kiwai believe in a vast number of Supernatural beings including various types of water beings, wicked female beings, and beings associated with certain localities. Virtually every conspicuous place in the landscape is thought to be the abode of a mythical being, some of which are humanlike and others of which are like animals or trees. Like many other groups in southern New Guinea, the Kiwai have a large number of myths about the life of Sido who the Kiwai believe was the first man to die and open the way to Adiri, the land of the dead.
Religious Practitioners. There are no priests and no specific training is necessary for those who perform religious ceremonies. Sorcery is learned on an individual basis from other sorcerers, and a sorcerer can demand, and will receive, almost any payment for his services. A common payment is sexual access to the client's wife. Sorcerers work by getting some part of their intended victim's body (e.g., nail or hair clippings) or personal possessions. According to Landtman, "every Kiwai man practices sorcery, without which he would have no success in any of his occupations or undertakings."
Ceremonies. The Kiwai have a large number of Ceremonies including ceremonies undertaken prior to a fight expedition and ceremonies designed to make young men fearless and invulnerable in battle. They also have several important secret ceremonies including the hóriómu, the mogúru, and the mimía. The hóriómu is connected with the cult of the dead and is held each year at the beginning of the dry season (in April or May). The ceremony lasts several weeks, occupying a few hours each day before sunset. The mogúru is the most secret and most important ceremony of the Kiwai People. Traditionally, it was held once or twice a year in the dárimo. The two main purposes of the mogúru are the sexual instruction of boys and girls who have reached puberty and the preparation of a magical concoction made of herbs and semen collected from the vaginas of women following promiscuous sexual intercourse. The mimía or fire ceremony is connected with the initiation of young men. During the Ceremony, the young men are burned and beaten and given magical substances that are believed to make them strong.
Arts. The Kiwai produce a great deal of representational art, and even their utilitarian wooden implements (e.g., digging or walking sticks) are often carved to represent a human face or body. Musical instruments include hourglass and cylindrical drums, rattles made from seed pods, reed whistles, panpipes, bamboo and reed flutes, shell trumpets, Jew's harps, and bullroarers. The Kiwai also make elaborate Ceremonial masks from wood and turtle shells.
Medicine. Illness is believed to be caused by comets, earthquakes, sorcery, or the abduction of a person's soul by a spirit. Menstrual blood is believed to be particularly deleterious to men's health. In the case of fever, the patient is bled from the part of the body where the illness is thought to be located. Sick people are given food that is considered "strong" such as pig meat, shark meat, taro, or sago. Bananas are not eaten because they are soft, and dugong and turtle meat may not be eaten because they are associated with the spirit world. It is also bad if a sick person comes into contact with someone (man or woman) who has recently had sexual intercourse.
Death and Afterlife. Wailing begins immediately after a person dies and continues through the night. The next morning, the dead person's face is painted black, white, and red and the body is dressed in a headdress and shell ornaments. The body is then placed in a sitting position near the door of the house. After being displayed, the body is placed on a board and carried a short distance from the village where it is placed on a platform. If the person was murdered and revenge has already been taken, the murderer's head may be cut off and placed as a pillow under the head of the deceased. Water is poured over the body daily to speed decomposition. When only bones remain, they are washed and then buried in a garden belonging to the dead person. Sometimes the skull of the deceased is kept and decorated by his widow. The widow spends a period of time secluded in an enclosure of mats in the móto. A widower will not go into seclusion, but he will spend several days crying for his wife and will refrain from hunting and fishing for a long time. Both widows and widowers wear a mourning garb made of grass and consisting of a cap with long fringe and a fringed covering for his or her shoulders, chest, arms, and legs. No drums may be beaten until a feast is held a few weeks later to end the period of mourning. Ordinarily the spirits of the dead are invisible, but sometimes they can be seen and touched. A ghost may not always start its journey to the land of the dead immediately but may instead linger for a time near its former home. The Kiwai are particularly afraid of the ghosts of sorcerers and persons who have met a violent death or have died in an unusual way. Even after spirits have gone to the land of the dead, they may return to give messages to the living either through dreams or appearing to them directly. Ghosts may also possess living people.