For Ralph in Chapter 12 of "The Lord of the Flies," the pig's head represents the raw and rapacious savagery of Jack and the hunters.
He argued unconvincingly that they would let him alone, perhaps even make an oulaw of him. But then the fatal unreasoning knowledge came to him again...These pained savages would go further anf further....A spasm of terror set him shaking and he cried aloud.....The skull [of the pig] regarded Ralph like one who knows all the answers and won't tell.
Ralph realizes that this act of posting a lifeless--or was it?--skull of a pig on a post represents the end of civilization in the hunters. As a result, he feels
his isolation bitterly....Lying there is the darkness, he knew he was an outcast.
Ralph also realizes that rationality has left the group led by Jack and he must try to survive their hunt of him:
He forgot his wounds, his hunger and thirst, and became fear, hopeless fear on flying feet....
As he stumbles over a root, he sees the shelter butst into flames ; then, he is down, rolling over and over in the sand, "crouching with arm to ward off, trying to cry for mercy' until the deus ex machina arrives in the form of a naval officer who has seen the flames and has come to rescue them.