In his essay on the invisible, 1 Clément Rosset dedicates a chapter to specters and ghosts. In the chapter, he refers to a Spanish tradition, referenced by the song in the epilogue, in which children who refuse to go to sleep are warned that they’ll be visited by the Coco—an indeterminate monster. If they don’t go to sleep, a horrible creature will appear and eat them up. What makes this variant so effective compared with other lullabies is that no one has ever seen the Coco. No one can actually describe what he looks like. He hasn’t been represented. This invisibility makes him all the more horrible, because everyone projects their own worst fears. Given the alternative, the best course of action is to go to sleep. There is, however, one depiction of the Coco in an engraving by Goya, where he appears as an ambiguous figure. There is nothing especially monstrous about him, except what we can’t see—his face and his body. The figure becomes terrifying because it remains hidden. The power of the invisible, of the in-between, is more gripping and effective than any explicit representation. The monster’s invisible state and its physical state—the children in the engraving who can see him do look horrified—are its most terrifying states, whereas its representation—what we as observers of the image experience—does not elicit the same fear.