The Secret Practice Record

When the heaven and earth first opened, the clear air rose up and became the Immortal Palace, while the turbid air sank and became the Nine Netherworlds, leaving only the "human gap" in the middle layer shrouded in gray mist. This fog is called "humid breath", which is not only the nutrient for the growth of all things, but also the poison that corrodes the spiritual wisdom. If a mortal forcibly absorbs the dark breath, the skeleton will develop coral-like "strange veins", and this is the beginning of the path of spiritual practice. Use the mortal body as a furnace, refine the dark breath as fire, and survive in the gap between alienation and sobriety.​