From Wikipedia: In practice the Hamatsa initiate, almost always a young man at approximately age 25, is abducted by members of the Hamatsa society and kept in the forest in a secret location where he is instructed in the mysteries of the society. Then at a winter dance festival to which many clans and neighboring tribes are invited the spirit of the man-eating giant is evoked and the initiate is brought in wearing spruce bows and gnashing his teeth and even biting members of the audience. Many dances ensue, as the tale of Baxbaxwalanuksiwe is recounted, and all of the giant man-eating birds dance around the fire.
Finally the society members succeed in taming the new “cannibal” initiate. In the process of the ceremonies what seems to be human flesh is eaten by the initiates. Boas describes the hamatsa initiate as eating actual human flesh without chewing. After the ceremony, the initiate is forced to drink large amounts of sea water to induce vomiting, thereby voiding the body of potentially harmful toxins. All persons who were bitten during the proceedings are given expensive presents, and many gifts are given to all of the witnesses who are required to recall through their gifts the honors bestowed on the new initiate and recognize his station within the spiritual community of the clan and tribe.