Here is a significant quote from the conclusion of Chapter 5:

A thin wail out of the darkness chilled them and set them grabbing for each other. The the wail rose, remote and unearthly, and turned to an inarticulate gibbering.

The significance of this passage shows how the boys' sense of power and control has broken down, engulfing them in fear. Despite their initial attempts to bring order to the island and find a way to survive and be saved, they are, after all, only children. Only moments before this occurrence, they had longed for the safety of adult authority. As Ralph said, "If only they could get a message to us . . . a sign or something."