I have a good story about this. I'm playing a sort of rough looking dude in a bar for a very small bet. A round or something, not enough to get anyone fighting over, as often happens in the bar pool realm. (I was young and dumb then and didn't mind the lousy bar atmosphere.) He looked like a guy who was decent at one time, but was having his struggles aiming. So I approach the table for my shot and notice what I think is the spot coming up. You know how the spot halfway peels up sometimes and you can stick it back down? So I started to, but fortunately before touching it I realized IT WAS A FRICKING HUMAN EYE. EEEEEEEEWWWWW.
Dude I'm playing lost an eye and now has a glass eye and he took it out of his head and put it on the table to shark me. I won anyway and collected my beer and the guy said he had no depth perception after losing his eye. Good enough proof for for me.