Rheum is a yellowish discharge, usually developing in the corner of the eye during sleep and "glueing the eyelids together." Rheum dries and gathers as a crust in the corners of the eyes or mouth, on the eyelids, or under the nose. It is formed by a combination of mucus (in the case of the eyes, consisting of mucin discharged from the cornea or conjunctiva), snot, blood cells, skin cells, or dust. Rheum from the eyes is particularly common, and is called "gound" or, in common usage, "sand" or "sleep." Normally, blinking causes gound to be washed away with tears. The absence of this function during sleep, however, results in a small amount of dry gound forming in the corners of the eyes even among healthy individuals, especially children. Still, the formation of a large amount of crust or the presence of pus within it may indicate dry eye or other more serious eye infections including conjunctivitis and corneitis. This man also suffers from trichotillomania (compulsive hair pulling) in his eyebrows.