A patch of cave wall opens like a mouth without teeth, throat, or anything usable by a body. So perhaps we should say that a patch of cave wall opens like the mouth on a flexible cloth puppet handled by an invisible expert lost in a room so dark that only the glow-in-the dark cloth of that mouth is visible, as well as the strange dark rough texture of the cloth visible beneath the glow.     That afternoon, out of the dark machinery, one of the dead of the future arrived.