Demon eyes are large floating eyes about the size of one's head. They appear only at night, and generally not near houses or people. They attack people and apparently eat them, although how is unknown, as they have no mouth. They actually have nothing to do with demons - I have no idea why they are named that, they just are. They appear in groups of 2, or in swarms that circle around the Brain of Cthulhu or Eye of Gramh.