Why does simon go to his bower in chapter 3 of lord of the flies?

Probably partially because he takes pity of the poor corpse which is being made to perform like a puppet, purely as an act of chance. This stops it from sitting up and behaving as if it were alive. Simon also intends to tell the other boys that it isn't a beast, just a dead body, and he knows that the lack of movement will stop the boys being scared and running away before they see that he is telling the truth. By coincidence untangling the parachute lines also allows the wind to carry the corpse away from the mountain top.