What can we infer about Ralph's nail biting in The Lord of the Flies?
For Ralph, nail biting marks a new awareness of the dangerous circumstances of his situation. This realization shows how Ralph's character matures, which is an important journey that young protagonists often undertake in literature and one essential to this novel's broader themes. In this particular case, the nail biting shows how Ralph loses the innocence of childhood by realizing the uncertainty that comes from knowledge.
Near the beginning of chapter seven, Ralph has a sudden realization of how dirty he is and how much he misses being clean, wishing for toiletries like soap and a toothbrush. When he suddenly looks at his nails he realizes: "They were bitten down to the quick though he could not remember when he had restarted this habit nor any time when he indulged it." Ralph is now marking the passage of time, which along with his desire to return to civilized society, shows how he is maturing. Unknown to him, he has already been making difficult decisions that manifest in the nervous habit of nail biting. Unlike several of the other boys, he now realizes the true dangers of their situation, which makes him a more capable leader but also a more thoughtful--and uncertain--individual.
This newfound maturity, though, also serves to distance him from the other boys who do not take their situation as seriously. It also creates friction between Ralph and Jack. In chapter eight, Ralph's leadership is directly challenged by Jack, who takes command by dissolving the group and leading most of the boys away to form his own group. Though Ralph becomes increasingly less assured as the novel progresses, he is now directly plunged into conflict that interferes with his decision making: "He broke off, frowning, thinking the thing out, unconsciously tugging at the stub of a nail with his teeth." His indecisiveness and uncertainty are manifesting, yet at the same time he is "thinking the thing out" even if he is nervous about events as he does so. Ralph has matured throughout the novel, and as he continues to develop he begins to act more like an adult, realizing that uncertainty is part of decision making and problem solving.
Later in chapter eight, we are told that "Ralph sat down and began to poke little holes in the sand. He was surprised to see that one had a drop of blood by it. He examined his bitten nail closely and watched the little globe of blood that gathered where the quick was gnawed away." This description of Ralph's nail both mirrors the current events of the plot and foreshadows what is soon to happen. His nail has been "gnawed away" just like his role as chief is taken away. He has lost his power like he has lost his nail. While the nail has been destroyed solely by him, Ralph is at least partially responsible also for his loss of leadership due to mistakes and errors in judgement, most notably his misjudging and underestimation of Jack and the other boys.
As Ralph continues to guide the few followers he has, he attempts to solve problems even with doubts and anxieties. Part of being an adult is recognizing and reflecting on one's own mistakes, as Ralph does. In addition to this, the "little globe of blood" that drops from his nail to the sand foreshadows the blood that will be spilled in the events that follow. There are more challenges ahead--potentially fatal ones--and Ralph must survive by learning from his mistakes and continuing to mature, which furthers his transition away from the naivety of childhood and into the stressful responsibilities of adulthood.
While children usually associate adults with complete knowledge and confidence, adults do not always know the correct answer or course of action. Because of this, they often make mistakes even if they think carefully or agonize about their decisions. When this happens, one must acknowledge their uncertainties and mistakes if they hope to learn from them. Over the course of the novel, Ralph has come to learn this fact of life. In essence, the nail-biting shows Ralph's coming-of-age as he learns that adulthood is not care-free, and that stress and anxiety are natural consequences of responsibility.