The actual nightmare element, though, was something more than this. It began with the living thing which presently entered through one of the slits, advancing deliberately toward him and bearing a metal box of bizarre proportions and glassy, mirror-like surfaces. For this thing was nothing human -- nothing of earth -- nothing even of man's myths and dreams. It was a gigantic, pale-grey worm or centipede, as large around as a man and twice as long, with a disc-like, apparently eyeless, cilia-fringed head bearing a purple central orifice. It glided on its rear pairs of legs, with its fore part raised vertically -- the legs, or at least two pairs of them, serving as arms. Along its spinal ridge was a curious purple comb, and a fan-shaped tail of some grey membrane ended its grotesque bulk. There was a ring of flexible red spikes around its neck, and from the twistings of these came clicking, twanging sounds in measured, deliberate rhythms.