The bizarre conversation between Simon and the Lord of the Flies confirms his belief that the Beast isn't a real creature but rather the evil that lurks within each and every one of the boys.

Simon's not like the other boys on the island; he has a deep connection to nature, and it's because of this connection that he's able to engage in a hallucinatory chat with a decaying, fly-blown pig's head on a stick.

The conversation's significance can also be seen in its foreshadowing of Simon's brutal death. The Lord of the Flies warns Simon that he will get angry if he stops the other boys from having fun. In due course, his anger—which is, of course, the evil lurking at the heart of everyone's souls—will manifest itself in Simon's savage murder at the hands of the other boys when they mistake him for the mythical Beast.

It's both ironic and tragic that Simon should've been able to confront the other boys' evil rather than the other boys themselves. Had they realized from the start that the Beast wasn't real—had they looked within themselves and seen the evil within their souls—then it's almost certain that Simon would not have come to such a sticky end.

Towards the end of chapter 8, Simon comes face to face with the Lord of Flies in his secluded spot in the forest. Simon proceeds to hallucinate and listens to the Lord of the Flies speak. During their conversation, the Lord of the Flies refers to Simon as a "silly little boy" and instructs him to run off and play with the others. The severed pig's head confirms Simon's belief by admitting that it is the beast. The Lord of the Flies goes on to say that it is part of Simon and the reason why "it's no go." Simon is too bewildered to respond, and the pig's head begins threatening him by saying,

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

The Lord of the Flies proceeds to warn Simon that he is going to get angry if he attempts to stop them from having "fun" on the island. Following the intense, enlightening conversation with the Lord of the Flies, Simon passes out on the forest floor.

The conversation between the Lord of the Flies and Simon is significant because the severed pig's head confirms Simon's belief that the beast is mankind's inherent wickedness. Unlike the other boys, Simon never believed that the beast was a tangible creature that could be hunted and killed. Instead, Simon knew that the real beast was the evil inside each boy, which underscores Golding's primary theme that mankind is inherently corrupt and sinister.

The Lord of the Flies also warns Simon that he will only find him "down there," which foreshadows his violent death at the hands of the other boys. In the next chapter, Simon attempts to inform the boys that the beast is actually the decaying corpse of a paratrooper. Tragically, the boys mistake Simon for the beast, are swept into a violent frenzy, and brutally murder him on the beach.

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 head of a pig on it as a kind of offering. Jack says, “This head is for the beast. It’s a gift.” Jack knows that he is helping his hunters to be less afraid by suggesting this token as some kind of appeasement for the imaginary beast they are all at least somewhat afraid of; however, it is literally just a rather gory pig's head on a stick.

Simon has seen the entire incident from his place of solitude, the place he goes when he needs to be alone. The first thing we learned about Simon is that he is prone to fainting, and the description of this conversation with what is called the Lord of the Flies suggests that it is all some kind of a waking dream. 

There were no shadows under the trees but everywhere a pearly stillness, so that what was real seemed illusive and without definition.... In Simon’s right temple, a pulse began to beat on the brain.

Th Lord of the Flies mocks Simon as a "silly little boy" for thinking that the beast on the island is "something you could hunt and kill." The final words the Lord of the Flies speaks to Simon are a threat, After mocking him and taunting him, the Lord of the Flies says:

“I’m warning you. I’m going to get angry. D’you see? You’re not wanted. Understand? We are going to have fun on this island. Understand? We are going to have fun on this island! So don’t try it on, my poor misguided boy, or else—”

What he is telling Simon is that anyone who tries to interfere with the unrestrained savagery which has been released on the island (the boys' own natural desires and inclinations) will not be tolerated. In fact, he says that if Simon tries to do anything to stop the savagery, Simon will be killed by "Jack and Roger and Maurice and Robert and Bill and Piggy and Ralph." It is a surprising list because Piggy and Ralph are Simon's friends, but it is a prophetic statement. Somehow Simon knows what is going to happen to him, and yet in the next chapter he still tries to warn them.

The final act in this scene is Simon's fainting, a reminder that this was not an actual conversation but more of a realization that the sensitive Simon is having with himself; he realizes that it is they who are the beast and it is their unrestrained human nature that has caused the evil on this island.