During the assembly held at night to put things back in order, Ralph opens up a discussion about "the beast," hoping to settle the matter once and for all so that they can "start again," and "be careful," and "be happy." However, the discussion has the opposite effect as the possibility of a "beast from water" begins to seem plausible. Simon, who is more sensitive and discerning than the other boys, but who has difficulty expressing himself in front of a group, rises to speak. He starts out by saying, "Maybe there is a beast," and the other boys interrupt him. He finishes his thought awkwardly, clarifying, "maybe it's only us." He is hoping to convey to the boys "mankind's essential illness," the fact that if the boys are in danger, it is from each other and from their own moral failures. His insights are spurned by the others.
In the next chapter, as the boys are searching for the beast that Samneric have seen, Simon remains in doubt about its existence as a physical creature. Even when he tries to imagine what type of creature it could be, "there rose before his inward sight the picture of a human at once heroic and sick." Whether he has in mind a political figure from his life back home, or Jack, whom he has acknowledged would be a poor alternative to Ralph as chief, he understands that humans are capable of producing far worse damage to society than beasts can. That is why he mumbles to Ralph, "I don't believe in the beast." He believes the real threat to the boys is the heart of evil that lies within each of them.
Ever since the first reference in Chapter Two of William Golding’s The Lord of the Flies of a “beastie,” a “snake-thing. Ever so big,” the image of a mythical beast captivates and haunts the boys. In Chapter Five of Golding’s novel, Piggy, trying hard to engage the group in a meaningful discussion, states: "I know there isn't no beast—not with claws and all that, I mean—but I know there isn't no fear, either." As the boys continue to debate the possibility and nature of “the beast,” Simon observes that “maybe there is a beast.” As the boys continue shouting each other down, he then adds, “What I mean is. . . maybe it’s only us.” What both Piggy and Simon are suggesting is the beast is a mythical representation of the deterioration of any vestiges of civil society that may remain among the young cast-aways. The “beast,” in other words, represents their fears of the unknown and the devolution of humanity back towards less civil and infinitely more violent times. No beast actually exists, of course, and the closest thing the boys discover to an aberrational presence on the island is the corpse of a parachutist. To the extent that civilization is giving way to anarchy, the beast represents the darker nature of mankind.
The most mystical and mysterious figure among the boys, Simon alone has a vague sense of the moral and spiritual conflict that has gripped them during their stay on the island. In chapter five, he suggests that "maybe there is a beast" but, also, that "maybe it's only us." Simon understands that it is not an outside evil but rather the outgrowth of "mankind's essential illness" that is destroying the group from within.
In chapter 5 and 6 Simon realizes that "the beast" represents the manifestation of evil that is accumulating within them. Therefore they arn't scared of the beast, but themselves, and what they will become.
This is further proved by the Lord of the Flies on page 158 when it says: "Fancy thinking the beast was something you could hunt and kill! You knew didn't you? I'm part of you? Close, close, close! Im the reason why its a no go? Why things are what they are?"