Demons

The other kind is a strange people; they possess no defined biology but these few unvarying characteristics: Whatever shape they take, their skin is a glossy black, dark as ink, and unlike the relative regular smoothness of our skin, their skin is covered with many dips and rises somewhat like the exaggeration of the wrinkles of one who overstayed a bath; They have no discernable eye or eyes; They each possess a throbbing heart. Some will simply feed on humans, but there have been cases of a sort of symbiosis between the other kind and man. In either case, it is imperative that agents not, we repeat, do not kill the other kind. The old treaty stands between us and them; woe on him who breaks the law.