Anyone who wants to develop the air kasióa should apprehend the sign in
air. And that is done either by sight or by touch. For this is said in the
Commentaries: “One who is learning the air kasióa apprehends the sign in air.
He notices the tops of [growing] sugarcane moving to and fro; or he notices the
tops of bamboos, or the tops of trees, or the ends of the hair, moving to and fro; or
he notices the touch of it on the body.”