To some it simply is an expression of the gentle swaying movement of grass on a windy day. The abundance of fringes and ribbons on the dress enhance the graceful movement of the dancers' bodies as they sway in the imaginary breeze.
Another tribe remembers dancing for the purpose of flattening the long prairie grass to prepare the ground for a larger tribal ceremony. To others, it originated to celebrate victory over an enemy.
Any one or all of these stories may be true.