First you become sensitive of three sounds, which is very difficult. And when you become so sensitive that you can drop the "A" and "M" and only the middle sound remains, in this effort you will lose your mind. You will be so much engrossed in it, so deeply attentive to it, so sensitive to it, that you will forget to think. And if you think, you cannot do this.
This is just an indirect way to bring you out of your head. Your mind is being focused on something very subtle. If you focus, you cannot go on thinking; mind will drop. Suddenly one day you will become aware what has happened.
