What do the boys realize at the beginning of chapter 2 of 'Lord of the Flies'?

After Ralph, Simon and Jack return from climbing the mountain the rest of the boys are informed that they are on an island which is probably uninhabited. They realise that there are no adults to tell them what to do. Jack tells them that there are pigs to hunt for meat while Ralph ensures that they realise that they need a signal fire to attract any passing ships or airplanes in order to be rescued. The small boy with the mulberry-coloured birthmark raises the issue of the "snake-thing/Beastie" and the boys begin to realise for the first time that perhaps everything is not quite as good as it first appeared.