What are the different boys' views of the beast?

The beast, of course, which doesn't exist, changes in the boys' imaginations. In Chapter 2, it begins as a "snake thing":

Ralph laughed... The small boy twisted further into himself.
“Tell us about the snake-thing.”
“Now he says it was a beastie.”
“Beastie?”
“A snake-thing. Ever so big. He saw it.”
“Where?”
“In the woods.”

Golding is always careful to let the reader know what the "beast" really is: in this case, it's simply vines:

“He says in the morning it turned into them things like ropes in the trees and hung in the branches."

In a later meeting, there's a suggestion that the beast comes from the sea, or even that the beast might be a ghost. Simon, in the same meeting, has it right: there is a beast, he says, but “What I mean is. . . maybe it’s only us.”

And the same thing happens later when the parachutist falls to the island, "beneath a parachute, a figure that hung with dangling limbs." This becomes, in the eyes of SamnEric,

“There were eyes—”
“Teeth—”
“Claws—”
“We ran as fast as we could—”
“Bashed into things—”
“The beast followed us—”
“I saw it slinking behind the trees—”

The key point here is that there is no consistency to the way the beast is imagined. Which makes sense: because the beast itself is entirely imaginary in any realistic way. The darkness which hides the "real beast" is, as Golding points out in the final paragraph of the novel, "the darkness of man's heart".