In The Lord of the Flies by William Golding, what appears during the heat of the afternoon?

In Chapter 4, Golding writes that strange things happened in the midday heat. The heat during the day is unbearable, and the boys relax underneath the shade of the forest trees. The glittering sea, coral reef, and palm trees seem to rise into the sky during the afternoon. Sometimes, the boys see imaginary land where there is none. Piggy is the only boy intelligent enough to realize that they are looking at mirages. The illusions appear to merge into the sky as the sun beats down heavily onto the island. At the end of the afternoon, the mirage subsides, and the horizon becomes level again. When the sun goes down and night falls onto the island, the children worry about the beast. Interestingly, both during the day and night, the boys' imaginations deceives them and their perception is altered.