Realization of the nature of the body becomes most vivid during old age and at death. Nobody wants to linger around a decomposing body. In this same vein, the Buddha advised his followers to actually contemplate the reality of the impurities of the body, that is, the bodily substances which, taken out of context, would be considered obnoxious. Specifically, that the body is simply a collection of hair, nails, teeth, skin, flesh, sinews, bones, marrow, kidneys, heart, liver, membranes, spleen, lungs, stomach, bowels, intestines, excrement, bile, phlegm, pus, blood, sweat, fat, tears, serum, saliva, mucus, synovial fluid, urine. Indeed, he actually prescribes a series of visual meditations on these realities.

From The Yoga Sutras of Patanjali, Translated with Commentary by Edwin Bryant, New York: North Point Press, 2009, p. 180.

Addendum (January 25, 2022)

Daniel Odier provides an even longer list of impurities in his Meditation Techniques of the Buddhist and Taoist Masters.[1] It can be found in Chapter 4, “Contemplative Techniques of Hinayana.”[2] In a section dedicated to the observation of the body, including observation of its impurities, he lists thirty-two substances: hair, body hair, muscles, nails, teeth, skin, sinew, bones, marrow, kidneys, heart, liver, serous membranes, spleen, lungs, intestines, mesenteries, stomach, excrements, brain, bile, digestive juices, pus, blood, oil, fat, tears, sweat, saliva, mucus, synovial fluids, and urine.[3]. By comparison, Bryant lists only thirty such substances. Interestingly, neither of the lists delves into male and female sexual organs and their juices. Alas, the Buddha and his followers can be a dash too chaste when it comes to the human body!

Footnotes

1. Rochester, Vermont: Inner Traditions, 2003 (first published in 1974).

2. Op. cit., pp. 67-94.

3. Op. cit., p. 71.