the beast struggled forward, broke the ring, and fell over the steep edge of the rock to the sand by the water."
Simon, trying to tell the boys the truth, stumbles into their circle. In their blind hysteria, they mistake him for the beast and brutally kill him.
The tragic irony is that Simon, the one person who knew the truth about the beast, is killed before he can reveal it. His death symbolizes the destruction of truth and reason.