Swami Muktananda has spoken about the So Ham mantra, which follows inhalation and exhalation. Osho spoke about bringing our attention to the gap or space between these breaths. Here Sri Vasant Lad explains the So Ham mantra that naturally accompanies our breath.
Osho too says the same. "Breath is the bridge. Not only is the breath a bridge to your body, but it is also a bridge between you and the universe. Breath is also the bridge between you, and space and time." Osho in his "Book of Secrets" says that "Buddha's enlightenment was based on using breath just as a technique to turn inwards - only this. Buddha said, "Be aware of your breath as it is coming in and going out." Eventually, we shall take notice of the gap or interval between two breaths without effort. In bringing us Shiva's first of nine techniques concerned with the breath, from the "Vigyan Bhairav Tantra", Osho in his "Book of Secrets" reveals, "If you can feel the gap, Shiva says, the beneficence, then nothing else is needed. You are blessed, You have known; the thing has happened."
Osho explains that contrary to our belief that the incoming breath and outgoing breath are running parallel as in parallel lines, they actually are one single breath, that in actuality flows in a circle. There is a point where the incoming breath turns and becomes the outgoing. Quoting another stanza of Shiva, we are asked to observe and realize this point of turning and becoming a realized soul. When the breath is static neither going out nor coming in, at this fusion point we are in our center. Agathiyar calls this center Suzhimunai. Each shall realize his center. It is the place where there arises energy and a feeling or Unarvu that comes with it. "Know it to be your Suzhimunai," says Agathiyar. Osho asks us to observe the child's breath. He says children are in their center and at their center. The reason is that children give themselves up completely in all their doings and at all times. Hence we should learn to follow these children give themselves up in totality and not try to change them to our ways. One who arrives at his center becomes total. Agathiyar calls this the state of Paripuranam.