When Simon wakes up, he meanders through the jungle until he reaches the mountain top; here, he sees a "humped thing suddenly sit up on the top and look down at him" (146). This vague figure is the dead parachutist that Golding describes in Chapter Six, "Beast from the Air:"
There was a speck above the island, a figure dropping swiftly beneath a parachute, a figure that hung with dangling limbs" (95).
The dead parachutist lands on the moutainin, still tethered to his parachute which catches in the wind causing the body to rise and fall. The boys see the silhouette of the figure and instantly jump to the conclusion that the 'odd creature' they see on the mountain top must be a fearsome beast.
The arrival of the dead parachutist is not without irony; in the previous chapter, the boys had wished for a grown-up to help them sort things out on the island. Golding grants their wish, but in a way that will only add the growing chaos.