"Because women so delicate so mysterious Father said. Delicate equilibrium of periodic filth between two moons balanced."
It was traditionally believed that women’s menstrual cycles were guided by the waxing and waning of the moon. Ovulation was thought to coincide with the full moon and menstruation with the new moon. The idea that menstruation is a curse which renders women unclean is ancient and widespread. See, for instance, Leviticus 15