When i was younger I always used to like skateboarding.Cause of a fashion-statement i didnt want shoestrings to be seen, so I layed the ends in the shoes,underneath mine soles.I had a same kind of feeling earlier with sand or little rocks undernearh feet when playing on the beach or in the dirt. The nerves on your soles are really sensitive (think about tickling ) I like the feeling when they are triggered constantly when i walk with no shoes on. It gives me uhhhhhh something i dont know what (its like an unrevealed secret of nature)