how do initiates make their selection at the choosing ceremony?

There are five large metal bowls in the room, each containing a substance that represents a faction. Abnegation's holds gray stones, Erudite's holds water, Amity's holds earth, Dauntless's holds lit coals, and Candor's holds glass. When someone chooses, she must use a knife to cut into her hand and sprinkle blood into the faction bowl of her choice.