The ejected parachutist was the dead man in Chapter 7 of the Lord of the Flies.
The man got ejected from a plane when it exploded. He landed on top of the mountain tangled in his parachute. Strong winds in the mountain made his corpse move forward in a bowing position then return to its original pose. This happened repeatedly.
The boys saw the corpse and its movements and they thought they were confronted by a live, predatory monster.
