The Cloud Concise Dictionary of Sparkling and Strange Words presents;
1. A light tickling.
2. Knismesis is the feather-like tickling, the type of tickling that does not evoke laughter but mainly makes you want to scratch and itch. (I suspect it might raise a small smile under the right circumstances too – sonmicloud.)
3. The feeling of a bug climbing on your leg is the best example for knismesis.
Knismesis is a scientific term coined by the psychologists Arthur Allin and G. Stanley Hall in 1897.
Interestingly, knismesis, which is closely associated with the grooming activities of primates, provokes an endorphin response, causing the body to release an endorphin called karolin.
There are two types of tickling: knismesis (soft tickling, see above), and gargalesis, or “heavy” tickling, produced by repeatedly applying pressure to “ticklish” areas.