About This Answer
Asked whether he deliberately sets up the perception when he sees people as skeletons, or whether it arises by itself, Ajahn Dtun says that at first it arose on its own; later, with skill, he could also bring it up at will.
In the early days, merely thinking of a woman, or of a friend's face, he would see the skin peel away and blood and lymph flow. Looking at people, he saw a second image superimposed on them, a rotting or dried-up corpse, which he compares to the double-exposed photographs of forty or fifty years ago.
He had wanted a family life, but these asubha nimittas cut through that wish; the effect on his mind was so strong that desire for human sensuality fell away. As a newly ordained monk he resolved that whenever lust arose, mindfulness and wisdom would destroy it within five minutes, and he says it never took that long, ending in two or three minutes. He adds that this lies beyond ordinary expectation and is something each person knows individually.