Ralph and Piggy are both on the island together. They find a conch and Ralph decides to blow it to alert everyone else. He takes the position as leader. They still think it's a joke and are just having fun.
The boys decide to light a fire on top of the mountain to signal passing ships. The fire spreads and kills someone. Ralph is starting to realize this isn't a joke anymore and they could actually be in danger.
Ralph is starting to establish rules. This is a pivotal moment because he is really starting to take control. He is realizing they might be stuck for forever if they don't take action and do something now.