A parietal eye is an organ on the top of the head of some lizards, frogs, and fish that's sensitive to light, likely "regulating circadian rhythmicity and hormone production for thermoregulation."  Whoa.  Typical wilderness conversation: 
Bob the Lizard:  Even though I'm not facing you, I can still sort of see what you're doing, Jimmy. 
Jimmy the Frog:  Shut up Bob.  I'll poke your three eyes out.
#science