Perhaps the most significant quote that sets up Golding's premise of 'throwing stones' occurs in chapter four, when Roger throws stones at young Henry, but chooses to miss:
"Roger gathered a handful of stones and began to throw them. Yet there was a space round Henry, perhaps six yards in diameter, into which he dared not throw" (62).
According to the narrator, Roger's arm has been conditioned by society. He undoubtedly got into trouble at some point in his former, civilized life for bullying other small children and now is very careful. In many ways, this scene with Roger and the stones reveals him for the predator he is. He waits until Henry is alone, carefully selects the stones, and then checks to make sure nobody is watching. Golding uses the scene with Roger to characterize him as a former bully, who is testing the boundaries and restrictions of his new environment to see what he can get away with. He will soon enough realize that those old boundaries are gone, and next time he aims with a stone, he will not miss.