In this scene, William Golding advances his novel's theme, provides significant character development for Jack and Roger, and foreshadows later events. This scene shows that the boys, far from being squeamish about hunting as in the first chapter, are beginning to take pleasure from cruelty and brutality. Chasing the wounded sow, the boys are "wedded to her in lust, excited by the long chase." When the sow collapses, "they were heavy and fulfilled upon her." Jack flicks blood at them, and they laugh. The brutal scene is a stark contrast to the sow's "deep maternal bliss" and the bright flowers and dancing butterflies of the field where the sow dies. The darkness in the hearts of the boys comes through powerfully.
Second, this scene shows how Jack is becoming more of a leader among his group. When he is able to track the sow by the trail of blood, the other boys "were awed by him and looked at each other in uneasy admiration." He is the one who cuts the sow's throat and guts it. Afterward, he gives orders to the boys, and he also demonstrates his leadership of the new pagan religion by leaving a gift for the beast. Roger's part in the kill is notable in that he shoves his spear up the sow's rectum in a move of torture, causing intense pain and squealing. The damage Roger does combines with Jack's knife to bring an end to the sow's life. When Jack starts giving instructions, Roger is the one who asks about fire, and he is on the team to steal fire from the other boys. The pairing of Jack and Roger as chief and chief henchman gets its real start here.
Finally, this scene foreshadows other scenes of brutality and cruelty that come later. At the end of the next chapter, Simon is murdered in a scene parallel to the boys all piling atop the sow. Later, Roger's cruelty grows when he throws stones at Ralph and Piggy, rolls the boulder onto Piggy, and tortures Samneric. Most importantly, when Samneric warn Ralph that Roger has "sharpened a stick at both ends," readers know what that portends because of the scene where the sow was killed. Thus the killing of the sow is a pivotal scene that displays Golding's theme of the boys' depravity, develops the characters of Jack and Roger, and foreshadows the danger the boys face later when Jack and Roger team up together to give full vent to the darkness in their hearts.
One of the primary reasons for the extended, horrific detail is so that the reader can grasp the descent into savagery into which the boys have sunk, but moreso in order that we may understand how brutal is the character of Roger. "Previously a strange loner, his personality has emerged as truly sadistic. Even more so than Jack, Roger loves the hunt for the pain he can inflict. He slowly drives his spear into the anus of the sow, torturing it more than killing it. This is the brutal extension of his previous torture of Henry on the beach."