In chapter eight of Lord of the Flies, by William Golding, Jack and his hunters sharpen a stick at both ends and place the dismembered, bloody head of a pig on it. Jack knows his hunters, like nearly all the boys on the island, have a fear of some nameless beast; he hopes to allay some of those fears by this act. He tells his hunters that they are leaving a sacrifice to appease the beast, though the reality is that the creature Simon sees as Lord of the Flies is really just a pig's head jammed onto a stick. Symbolically, the pig's head is much more than that.
Simon has a hiding place where he goes to be away from everyone, and he is there when the hunters erect the faux sacrifice right outside of his secret hideaway. We know that Simon has a tendency to faint, and through the course of his conversation with the Lord of the Flies we have indications that this dialogue is not real but conducted in Simon's head. At the end of the conversation Simon faints.
The Lord of the Flies tries to intimidate and threaten Simon; he calls Simon "just an ignorant, silly little boy" and mocks Simon for thinking the beast is "something you could hunt and kill!" Golding uses this symbolic beast, the Lord of the Flies, to reveal the truth to Simon: they, the boys, are the beast. The Lord of the Flies says,
“You knew, didn’t you? I’m part of you? Close, close, close! I’m the reason why it’s no go? Why things are what they are?”
Before Simon faints, the Lord of the Flies warns Simon that he is not wanted on this island (because Simon represents the soul and spirit of man) and predicts that "Jack and Roger and Maurice and Robert and Bill and Piggy and Ralph" will kill him. And they do.