Well, as the narrator observes, "[the villagers] still [remember] to use the stones" (76). Not only is stoning a particularly horrifying way to imagine dying, it's also, always, a crowd-generated death. In other words, stones allow everyone in the village to participate freely in the ritual, from the youngest children to Old Man Warner. Stones are also significant as murder weapons because the first human tools were made of stone; this lottery really does seem to have its ancestors in the earliest type of violent human ritual. What's more, stoning comes up specifically in the religious texts of all three of the Abrahamic religions: Christianity, Judaism, and Islam. So it's not just an early form of murder; stoning has a strong religious association with community punishment of abomination; in other words, stoning is the classic means for expelling an outsider to reinforce group beliefs.