About This Answer
Should the 32 parts of the body be contemplated all at once, or one at a time? Ajahn Dtun answers that reflecting on them all at once is not really possible. One chooses whichever part the mind is inclined towards and stays with it long enough to see its nature clearly: its loathsomeness, impermanence and absence of self. Seeing this can give rise to disenchantment, and the mind puts that part down.
Someone might reflect on the hair until the mind lets go, yet doubt about the body remains, so they move to the skin, and the same may happen again. In this way the mind can keep moving through the body. The 32 parts simply keep contemplation within the confines of the body; one contemplates whatever part the doubt arises around or wherever one wishes to go.