Yoga is all about the breath, the pranayama. If one can breathe, one can do yoga; it is as simple as that. How we breathe can act as a prescription for us, which brings us to kriyas.
Kriyas are certain movements, postures, and types of breathing which, when combined, serve as prescriptions for desired outcomes.
One very beneficial type of breathing done during kriyas is the Whistling Breath. Whistling can change circulation, creates balance, stimulate the vagus nerve, relieve one of stress and tension, and is both breath and music combined, which is called naad swaras.
Each kirya will offer specific instructions on whether the whistle is executed on the inhalation, the exhalation, or sometimes, for both.
To whistle on inhalation: pucker the lips and concentrate on the third eye point or where the instructions ask the yogi to concentrate. As the inhale is initiated through the mouth, make a high-pitched sound as the air moves through and then exhale through the nose. Be sure to listen to the sound of the whistle on the inhale and the sound of the soft breath leaving the nose on the exhalation.
To whistle on exhalation: inhale through the nose and exhale through puckered lips, making a high-pitched sound with the lips. Again, focus on the third eye point unless the directions dictate otherwise, and be sure to focus the ears on the sounds of the whistle and the breath.