G. Stanley Hall in the context of "Tickle"

Tickling is the act of touching a part of a person's body in a way that causes involuntary twitching movements or laughter. The word "tickle" 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.

Psychodynamics, also known as psychodynamic psychology, in its broadest sense, is an approach to psychology that emphasizes systematic study of the psychological forces underlying human behavior, feelings, and emotions and how they might relate to early experience. It is especially interested in the dynamic relations between conscious motivation and unconscious motivation.

The term psychodynamics is sometimes used to refer specifically to the psychoanalytical approach developed by Sigmund Freud (1856–1939) and his followers. Freud was inspired by the theory of thermodynamics and used the term psychodynamics to describe the processes of the mind as flows of psychological energy (libido or psi) in an organically complex brain. However, modern usage differentiates psychoanalytic practice as referring specifically to the earliest forms of psychotherapy, practiced by Freud and his immediate followers, and psychodynamic practice as practice that is informed by psychoanalytic theory, but diverges from the traditional practice model.

Lewis Madison Terman (January 15, 1877 – December 21, 1956) was an American psychologist, academic, and proponent of eugenics. He was noted as a pioneer in educational psychology in the early 20th century at the Stanford School of Education. Terman is best known for his revision of the Stanford–Binet Intelligence Scales and for initiating the longitudinal study of children with high IQs called the Genetic Studies of Genius. As a prominent eugenicist, he was a member of the Human Betterment Foundation, the American Eugenics Society, and the Eugenics Research Association, believing in genetic racial associations with intelligence. He also served as president of the American Psychological Association. A Review of General Psychology survey, published in 2002, ranked Terman as the 72nd most cited psychologist of the 20th century, in a tie with G. Stanley Hall.

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 Ancient Greek κνισμός (knismós) meaning 'itching'. The term gargalesis stems from the Ancient Greek γαργαλίζω (gargalízō) meaning 'to tickle'. The suffix -esis is used to form nouns of action or process.