Acting on his darker impulses, at first in small ways, [Roger] knocks over Percival and Johnny's sand castles. Then he throws stones at Henry, only missing because his arm "was conditioned by a civilization that knew nothing of him and was in ruins."
This scene portrays Roger as an evil person. He is clearly trying to hurt someone. He has evil intentions:
Secretive and gloomy. He throws stones at Henry to intimidate him, relishing the freedom to be mean. He represents the aspect of a person who out of past resentments at being disciplined by elders lashes out cruelly when free from restraint.
As later we will see, Roger has a cruel side to him. His actions create tension and foreboding of evil yet to come. It is as if Roger has some evil inside of him. He proves his evil side when he puts his spear in the sow's anus and twists until the sow is screaming in anguish and pain:
They corner the wounded pig, and when she falls they are on her. Roger is particularly cruel, driving in his spear slowly by leaning his weight upon it until the sow screams in agony.
Later, Roger intentionally sets out to harm Piggy. He intentionally pushes a boulder at Piggy, thus pushing Piggy to his death. In the end, Roger is helping Jack chase Ralph. There intentions are to kill Ralph:
[Roger] prepares a stick, with points sharpened at each end, on which to mount Ralph’s head.
The mood is ominous and foreboding. When will the killing stop?