What are the reasons for Ralph's fingernails being 'bitten down to the quick?
Golding uses the detail of Ralph's fingernails being chewed on to indicate Ralph's nervous state. For many people, Ralph included, fingernail chewing is a nervous tic, a way for him to cope with the stress of a situation. He gets nervous, so he chews his fingernails down. This detail is interesting, because it is also exactly the sort of bad habit that parents would frown upon. Had Ralph gotten a scolding from his mother for chewing his fingernails? He probably has; it is a childish habit, but one hard to break, and the fact that Ralph is reverting back to his old habits like nail-biting, and then later he mentions he will probably be "sucking [his] thumb next," suggests that Ralph is really stressed out; these habits are one way for him to diffuse all of his pent-up emotions. The notion of him sucking his thumb really suggests that he yearns for the comfort of his early childhood and the security of his parents.