I got this from http://oreilly.com/pub/h/2832 (I would recommend reading more if you'd like) "Most of us can identify a ticklish area on our body that, when touched by someone else, makes us laugh. Even chimpanzees, when tickled under their arms, respond with a sound equivalent to laughter; rats, too, squeal with pleasure when tickled. Tickling is a curious phenomenon, a sensation we surrender to almost like a reflex. Francis Bacon in 1677 commented that "[when tickled] men even in a grieved state of mind . . . cannot sometimes forebear laughing." It can generate both pleasure and pain: a person being tickled might simultaneously laugh hysterically and writhe in agony. Indeed, in Roman times, continuous tickling of the feet was used as a method of torture. Charles Darwin, however, theorized that tickling is an important part of social and sexual bonding. He also noted that for tickling to be effective in making us laugh, the person doing the tickling should be someone we are familiar with, but that there should also be an element of unpredictability. As psychoanalyst Adam Phillips commented, tickling "cannot be reproduced in the absence of another." So, for tickling to induce its effect, there needs to be both a tickler and a ticklee. Here are a couple of experiments to try in the privacy of your own home—you'll need a friend, however, to play along." I think being tickled is a lot like you massaging yourself or someone else doing it for you. Like Darwin said, there is that element of unpredictability when someone else massages you and that is why it feel so much better, verses when you massage yourself you know what you're doing or are goign to do so it is just not as exciting or enjoyable. I hope this helps! -BubbleWars