In Lord of the Flies, it is one of the younger boys who first raises the issue of a snakelike "beastie." Ralph responds rationally that there will not be any large predators on such a small island. The beast is a figment of their imagination. This, however, is just why belief in the beast becomes so popular. The boys' imaginations understandably run riot on the island. It is all too easy to believe that something terrifying lives there.
It is Simon who discovers the true nature of the beast, in a series of ironies. He finds that the physical object they thought was the beast is, in fact, the corpse of a parachutist. However, he also has an imaginary conversation with the Lord of the Flies, a pig's head on a stick which Jack has set up as an offering to the beast. Although the conversation is a delusion, the point the Lord of the Flies makes about the beast is true. The beast is part of Simon and all the other boys. It is stronger in some than in others—Jack and Roger are possessed by it—but it is present in all of them. They are the most terrifying thing on the island. Soon afterwards, the other boys mistake Simon for the beast and beat him to death, proving this point.