This happens in Chapter 8.
“What are you doing out here all alone? Aren’t you afraid of me?”
Simon shook.
“There isn’t anyone to help you. Only me. And I’m the Beast.”
Simon’s mouth labored, brought forth audible words.
“Pig’s head on a stick.”
“Fancy thinking the Beast was something you could hunt and kill!” said
the head. For a moment or two the forest and all the other dimly appreciated
places echoed with the parody of laughter. “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?”
The laughter shivered again.
“Come now,” said the Lord of the Flies. “Get back to the others and
we’ll forget the whole thing.”
Simon’s head wobbled. His eyes were half closed as though he were
imitating the obscene thing on the stick. He knew that one of his times
was coming on. The Lord of the Flies was expanding like a balloon.
“This is ridiculous. You know perfectly well you’ll only meet me down
there—so don’t try to escape!”