Why doesn't Roger hit Henry with the stones?

Roger throws hard nuts at Henry. Roger aims to miss Henry because his arm is still conditioned by the old world. Somewhere in his brain, though fading fast, was the reprimands of parents, teachers and authority figures. Roger is a sociopath who is discovering that the live between civilized behavior and savagery is quickly disappearing. Roger wants to hurt Henry, he derives enjoyment out of inflicting pain on others. Roger personifies the darkness that is taking hold of the boys on the island.