That's what happens when mathematicians get haircuts. The guy basically asked for a 3D graph of a partial differential equation to be cut into his hair. The barber, clearly a fellow math enthusiast, immediately understood and delivered a colorful representation of the function's surface. For the uninitiated, that equation is a second-order PDE involving mixed derivatives. It's the mathematical equivalent of asking your barber to perform brain surgery with scissors. The resulting rainbow graph haircut is what happens when you let equations determine your style choices. Next time just ask for "a little off the top" like a normal person. Your barber might be talented, but turning your head into a calculus textbook illustration is pushing it.