As Angels, Demons function on Essence provided by the God-Machine, the ephemeral stuff of the Shadow that also feeds spirits. Once an Angel falls and is cut off from the God-Machine's supply, he can see Aether emanating from the engines of their Creator. Human physics understands the concept as entropy: the fact that in any reaction a certain amount of energy is lost as waste heat. Demons know that the same principle applies to the occult physics of the God-Machine and its Infrastructure, and have found ways of exploiting that form of waste heat for themselves.