Percy packs a stone into the snowball that accidentally strikes Mary Dempster’s head instead of Dunstan’s. At the end of the novel it is revealed that Dunstan has kept this stone his whole life, unwilling or unable to discard it. This stone is finally placed (presumably by Paul) into the mouth of Boy Staunton after his murder (which is made—by Paul—to look like a car accident). The stone is a symbol for Dunstan’s enduring guilt and sense of responsibility, as well as a symbol for Boy’s complete ignorance and lack of responsibility. In this way it functions more generally as a symbol for the disparity in individual experience. The event containing the stone—the throwing of the snowball—is perceived completely differently by Dunstan and Boy. While it almost mystically shapes Dunstan’s whole life, it doesn’t even exist in Boy’s memory at all. In a novel so dedicated to examining history and its meaning, the stone serves as a reminder that history is filtered through the psyches of the individuals who experience it.