What embarrasng thing does Ralph say to imself near the beginning of the chapter that he's afrad someone might have overheard?What does he mean by it? What change in Ralph does the act of talking to hmself demostrate

“Be sucking my thumb next—”

Ralph was noticing that he'd started biting his nails again while on the island..... something he hadn't done since he was a little boy. The comment doesn't really mean anything more than, "what's next". Talking to himself leads me to believe he really doesn't feel as if he has anyone else to talk to.