This episode occurs in Chapter 8 "Gift for the Darkness," and it is related in such a way that we react with horror and disgust. Sexual, or more accurately rape-like, diction is used in this scene to show the devolvement of the boys into savagery. We see here no noble man versus beast conflict; instead, we have a nursing, bleeding sow portrayed as the victim of the boys' frenzied bloodlust:
Here, struck down by the heat, the sow fell and the hunters hurled themselves at her. This dreadful eruption from an unknown world made her frantic; she squealed and bucked and the air was full of sweat and noise and blood and terror.
This episode is one of a series of parallel scenes in which a killing of an animal is involved. The first killing of a pig is barely mentioned as Jack and his tribe kill this one just as a ship passes by the island. The second scene involves the killing of a boar. This is the third one, and the most savage. The next hunt, of course, is a manhunt with Ralph as the prey.
The "trophy" of this hunt is the pig's head that is placed on a stick. It left to appease the beastie, in another savage ritual. This pig's head becomes a major symbol of evil and temptation in the novel, as it is this pig's head that talks to Simon urging him to "play" like the others.