If in the name of kayanupassana one sits with closed eyes and simply names or imagines the different parts of the body, such a person is far away from the correct practice of Vipassana, from the direct exploration of truth. Therefore awareness of physical sensation is indispensable to the practice of kayanupassana. Sensations exist, of one type or another, at every moment on every part, every atom of the body. One must develop the ability to feel them consciously in order to understand the entire truth of the body. Sensations can be experienced only within one's body, and the reality of body can be experienced only by means of sensations.
Sensation overlaps the two fields of mind and matter.
For this reason observation of sensation, as we shall see, is a way to explore the mental-physical phenomenon in its entirety. In the practice of kayanupassana, observation of sensations will enable the meditator to experience directly the changing nature of the physical structure. By examining every part of the body in turn, one realizes that all sensations arise and pass away. As one repeats this practice, eventually a stage comes in which one experiences the instantaneous dissolution of every particle of the body. Particles arise with the predominance of one or more of these elements, giving rise to the infinite variety of sensations.