DORA: What do you call this gunk in the corner of my eye?
WENDELL: Ah..."gunk" is good; "crust" would be okay; "sleepies" is also common. There's no official name for the stuff. It's just the pasty stuff that appears in the corners after a long night's sleep and the Sandman's stopped by.

DORA: Well, what is eye gunk, anyway?
WENDELL: Goop, wonderful goop. All night things are dripping into your eyes.
DORA: What kinds of things?
WENDELL: Sweat, oil and, most especially, tears. When you're awake your eyelashes work like windshield wipers, removing the tears that drip down from over a dozen tubes above your eyes. But when you're asleep they're not working.
DORA: Windshield wipers? Are you kidding me, Wendell?
WENDELL: Nope, all night long, a goopy mix of tears, sweat and oils from other glands accumulates near the caruncle, the fleshy bump in the commissure, or corner of your eye. Without your windshield wipers, and with your eyes shut, your tears can't drain as easily into the tear ducts below your eyes. By morning, the mixture has begun to dry into a nice crust!

DORA: But why do we have tears in the first place?
WENDELL: If worms had eyes, I'd demand that we have tears. Why? Tear fluid, which is continually dripping from your tear glands, keeps your eyes clean and moist.
DORA: But what about my tears of joy and tears of sorrow. Do they come from the same place?
WENDELL: Yup. Your emotions come from a different place, obviously, but your tears that result drip down from the same tear ducts. The only difference is that when you cry, instead of a few tears, there is a flood of them. You simply have too many tears for your tear ducts to drain them all! So they end up rolling down your cheeks, instead.

DORA: So what are these tears made of?
WENDELL: Salts, sugar, ammonia (like the stuff people clean with), urea (as in the stuff in urine), lots of water, albumin, citric acid (as in what's in lemons and oranges), and lysozyme (a chemical that kills bacteria).