Knismesis and gargalesis are the scientific terms, coined in 1897 by psychologists G. Stanley Hall and Arthur Allin,[1] used to describe the two types of tickling.
[2] Gargalesis refers to harder, laughter-inducing tickling, and involves the repeated application of high pressure to sensitive areas.
Knismesis can also be triggered by crawling insects or parasites, prompting scratching or rubbing at the ticklish spot, thereby removing the pest.
It is possible that this function explains why knismesis produces a similar response in many different kinds of animals.
[7] For example, ultrasonic vocalizations described as "chirping", which play into social behavior and even have therapeutic effects, are reported in rats in response to human tickling.