In Lord of the Flies, what is the "beast from air" described in chapter 6? Who discovers it and how do they react?

The "beast from air" in chapter 6 is ironic because in chapter 5 the boys believe there is a "beast from water," but those fears are groundless. The boys at the beach fall sound asleep after having been startled by a littlun having a nightmare. Meanwhile, Samneric, the twins, are keeping night watch on the mountain, ostensibly keeping the fire burning. However, they fall asleep as well, and while they sleep, an air battle rages overhead, part of the world-wide nuclear war that resulted in the boys' landing on the island. A paratrooper, killed before or during his jump, lands on the island. The parachute fills with wind, causing the corpse to be pulled up the island. 

Samneric wake up and tend to the fire. While Sam's back is turned to the paratrooper, Eric sees the movement and hears the sound of the fabric. Eric screams at Sam, and he comes around the other side of the fire to see it. Hugging each other tightly, they are frozen in fear for about ten seconds. Then they careen down the mountain and wake Ralph up to tell him they have seen the beast.