Scientists have discovered that the feeling experienced when we are tickled causes us to panic and is a natural defense to little creepy crawlers like spiders and bugs.
The tickle response may be a protective warning device against the stings and bites of harmful insects. That same ticklish feeling sends us into a state of panic and causes a response of uncontrollable laughter if a person tickles us.
Tickling was and is an ingredient in forming and keeping social bonds. Such bonding occurs through stimulating each other to laugh and feel merry. This is particularly true for parents and children.
The threat of being tickled without laying a finger on them is enough to induce hysterics. This is as effective with adults as with children and provides a clue to the fact that tickling is not merely a physical sensation
You cannot tickle yourself. If you try, you will not succeed since there is no surprise or lack of control in the stimulation.
As a slightly off track note, tickling was used as a method of torture by the ancient Romans.
hehe, see tickling is evil.