<unk>  The Baby by Fritz Zuber-Buhler<unk>  is the act of touching a part of a body in a way that causes involuntary twitching movements or laughter. The word evolved from the Middle English tikelen, perhaps frequentative of ticken, to touch lightly. In 1897, psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena. One type is caused by very light movement across the skin. This type of tickle, called a knismesis, generally does not produce laughter and is sometimes accompanied by an itching sensation.
Tickling
Tenderness 
Allodynia
Erythema
Retching
Palsy
Irritation
Chromesthesia