Simon is the most spiritual of the boys on the island. He is filled with goodness and is often understood as the novel's Christ figure. He stands for conscience and morality.

Therefore, it is not surprising that he is able to communicate with the Lord of the Flies, the pig's head on a stick surrounded by buzzing flies. This pig's head symbolizes the evil that Jack has unleashed in himself and the others.

In a hallucinatory conversation Simon has with the pig's head, Simon intuits that, as the pig says, even he, Simon, has the Lord of the Flies's evil impulses residing in his soul. The Lord of the Flies says to him,

You knew, didn’t you? I'm part of you?

This is significant in making explicit an important theme of the novel: that the capacity for evil lies within the human psyche. It is not "out there" in a mythical "beast" but is part of the aggressive, atavistic, sadistic tendencies that all humans must learn to control to be part of civilization.

The Lord of the Flies makes clear that evil wants no part of a person like Simon. His conscience and decency only get in the way of the boys' unleashing their most atavistic impulses in order to have "fun." The head says to Simon,

You’re not wanted. Understand? We are going to have fun on this island. Understand?

Fancy thinking the Beast was something you could hunt and kill!

You know perfectly well you’ll only meet me down there—so don’t try to escape!

We are going to have fun on this island! So don’t try it on, my poor misguided boy, or else.

The conversation Simon has with The Lord of the Flies is significant because not only does it foreshadow Simon’s death but it also reveals what the beast really is. The Lord of the Flies confirms what Simon already knows: that the beast is in each of the boys. The conversation is one-sided, with the beast doing the talking. This symbolizes that eventually the brutal nature of the boys will take control, and there will not be a rational voice to be heard. The fact that Simon merely stares mutely at the beast and is unable to answer represents the boys’ inability to stand up for what is right. Ultimately they will fall under Jack’s violent control and will be unable to stand against him. They are mute against what they know is morally right. At the end of the conversation, Simon is inside the mouth of the beast and falls unconscious. This shows the progression of the theme that evil lies within every person, and if that evil is not confronted, it will consume everything in its path.

Throughout the conversation the beast becomes more agitated and aggressive towards Simon. This symbolizes the progression of violence to come on the island. The mocking tone of the beast as he calls Simon an “ignorant, silly little boy” mirrors the many times that the boys have mocked Piggy and his rational ideas. Progressively, the beast becomes more menacing until finally it states that Simon will die by the hands of Jack, Roger, Maurice, Robert, Bill, and Piggy and Ralph. The order of the names is important because it shows that no one is immune to the power of the beast. Some may be able to resist it to an extent, while others embrace it and use it to their advantage.