After spending about two hours in a hot tub the other night and therefore having excessively pruney hands, the question that I've always been curious about came to mind: why does our skin get pruney when it's been under water for a long time? I looked up some things, and discovered that at first, scientists believed that it was simply due to the different layers of skin we have. The outermost layer of the outermost layer of our skin has cells that are filled with keratin, a protein that keeps your skin hydrated by absorbing a lot of water. When underwater, the keratin absorbs a lot of water, expanding the cells and thus expanding the size of the skin layer. Since the second outermost layer doesn't expand, the outermost layer has to fold in order to adjust to the new size difference. This made perfect sense until it was discovered that people with severed nerves don't get pruney, which leads to the claim that our nerves "tell" our skin to get pruney. When our nerves sense that our skin is underwater for a long time, information is transferred along the neural pathways to "fold" our outermost layer of skin in order to increase the mew of our skin and thus increase the force of friction between our hand and whatever we touch (since F(f) = (mew)F(n)), thus giving us better grip in order to fight against the now slipperiness that the water on our hands creates. It's crazy how intelligently our bodies were created!