When Simon tries to visualize what this beast might look like, "there arose before his inward sight the picture of a human at once heroic and sick" which is a depiction of Golding 's vision of humanity as flawed by inherent evil.
Simon was unable the night before to make the other boys see his outlook; even Ralph, with his new appreciation for thought and wisdom, dismisses Simon without considering that he may have valuable insight.
Yet that night, "a sign came down from the world of grownups" that is frightening and mysterious and changes the entire complexion of the group for the worse. Above them an aerial battle is taking place. The other boys start swarming into the rocks, having a grand old time, until Ralph realizes the signal fire has gone out again.
When they get to the mountain, Ralph expresses concern about maintaining the signal fire. It even has boulders, which, if pushed in the right way, could roll down to crush approaching enemies.
When Sam and Eric wake up, they tend to the fire to make the flames brighter.