Foreshadowing lets the reader know about something that will happen in the future. How is the following line an example of this:"Later perhaps, practiced debaters- Jack, Maurice, Piggy- would use their whole art to twist a meeting..."

This is when Ralph needs to lay down the law. He says that later the meanings of his rules will be twisted in debate. I'm not sure what this foreshadows. If anything it is foreshadowing irony in the fact that there will be no more debate or argument; Jack will control everything.