Knismesis and gargalesis are the scientific terms, coined in 1897 by psychologists G. Stanley Hall and Arthur Allin, used to describe the two types of tickling. Knismesis refers to the light, feather-like type of tickling. This type of tickling generally does not induce laughter and is often accompanied by an itching sensation. Gargalesis refers to harder, laughter-inducing tickling, and involves the repeated application of high pressure to sensitive areas.
While the two terms are used in academic papers, they do not appear in many dictionaries and their origin is rarely declared. The term knismesis comes from the Greek knismos meaning 'itching'. The term gargalesis stems from the Greek gargalizo meaning 'to tickle'. The suffix -esis is used to form nouns of action or process.