In Lord of the Flies, who is the only one who can interrupt someone speaking?

The conch shell is a symbol of rules, order, and stability. Whoever has it possesses the right to speak and cannot be interrupted by the others. All except Ralph, of course, whom the boys have chosen as their leader. For Jack, this is all very frustrating. He doesn't believe in anything that smacks of democracy; he wants to be dictator and to boss everyone around. But so long as the convention of the conch shell is respected there's not much he can do about it.

Fortunately for Jack—and unfortunately for everyone else—this little experiment in democracy doesn't last for very long. Gradually the boys begin their descent into savagery and outright barbarism, with Jack fulfilling his wish to be dictator of the island. The democratic authority represented by the conch ebbs away over time, but when the conch is dashed against the rocks along with Piggy, it's destroyed forever.

The only one who is allowed to speak is the person holding the conch shell. No one is to interrupt the person speaking if he is holding the shell except for Ralph because he is elected to be the leader. This rule, however, does not last because the boys lose their sense of civility as the story goes on.