I could spawn a whole new thread on feet. Like I mentioned before, the nerve density in feet is incredibly high. They're designed to feel and to respond to sensations very rapidly. When we spend all day in shoes, those nerves become overly sensitive (which, IMHO, is a part of the reason why so many people have ticklish feet), but when we let them feel the world around us, the proprioception they develop is really cool. The neural feedback can be so strong that it's easy to see why people tend to either love or hate foot play, but that there's rarely a middle ground.
It's kind of a shame we let them marinate in warm, humid bacteria/fungus farms all day long.