Last updated
Tickling The Baby by Fritz Zuber-Buhler Zuber Buhler Fritz Tickling The Baby.jpg
Tickling The Baby by Fritz Zuber-Buhler

Tickling is the act of touching a part of a body in a way that causes involuntary twitching movements or laughter. [1] The word Loudspeaker.svg "tickle"   evolved from the Middle English tikelen, perhaps frequentative of ticken, to touch lightly. [1]


In 1897, psychologists G. Stanley Hall and Arthur Allin described a "tickle" as two different types of phenomena. [2] 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.


James John Hill James John Hill (circle) Being tickled.jpg
James John Hill

Tickling results from a mild stimulation moving across the skin, and is associated with behaviors such as smiling, laughter, twitching, withdrawal and goose bumps. The tickle can be divided into two separate categories of sensation, knismesis and gargalesis. Knismesis, also known as a "moving itch", is a mildly annoying sensation caused by a light movement on the skin, such as from a crawling insect. This may explain why it has evolved in many animals. [3] Gargalesis reactions refer to a laughter-provoking feeling caused by a harsher, deeper pressure, stroked across the skin in various regions of the body. [3] These reactions are thought to be limited to humans and other primates, although some research has indicated that rats can also be tickled in this way. [4] A German study also indicates that the gargalesis type of tickle triggers a defense mechanism for humans in the hypothalamus conveying submissiveness or fleeing from danger. [5]

It appears that the tickle sensation involves signals from nerve fibres associated with both pain and touch. In 1939, Yngve Zotterman of the Karolinska Institute studied the knismesis type of tickle in cats, by measuring the action potentials generated in the nerve fibres while lightly stroking the skin with a piece of cotton wool. Zotterman found that the "tickling" sensation depended, in part, on the nerves that generate pain. [6] Further studies have discovered that when the pain nerves are severed by surgeons, in an effort to reduce intractable pain, the tickle response is also diminished. [7] However, in some patients that have lost pain sensation due to spinal cord injury, some aspects of the tickle response do remain. [8] Tickle may also depend on nerve fibres associated with the sense of touch. When circulation is severed in a limb, the response to touch and tickle are lost prior to the loss of pain sensation. [9]

It might be tempting to speculate that areas of the skin that are the most sensitive to touch would also be the most ticklish, but this does not seem to be the case. While the palm of the hand is far more sensitive to touch, most people find that the soles of their feet are the most ticklish. [9] Other commonly ticklish areas include the underarms, sides of the torso, neck, knee, midriff, perineum, [10] navel, ribs, breasts, and genital area.

Some evidence suggests that laughing associated with tickling is a nervous reaction that can be triggered; indeed, very ticklish people often start laughing before actually being tickled. [11]

Social aspects

Francois Boucher - Le sommeil interrompu Francois Boucher - Le sommeil interrompu.jpg
François Boucher – Le sommeil interrompu

Charles Darwin theorized on the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure. [12] If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance, and reasoned that this is why some people cannot effectively tickle themselves.

Darwin explained why we laugh when we are tickled by saying, "The imagination is sometimes said to be tickled by a ludicrous idea; and this so-called tickling of the mind is curiously analogous with that of the body. Laughter from being tickled [is manifestly a] reflex action; and likewise this is shown by the minute unstriped muscles, which serve to erect the separate hairs on the body". [13]

Tickling is defined by many child psychologists as an integral bonding activity between parent and children. [14] In the parent–child concept, tickling establishes at an early age the pleasure associated with being touched by a parent with a trust-bond developed so that parents may touch a child, in an unpleasant way, should circumstances develop such as the need to treat a painful injury or prevent harm from danger. [14] This tickling relationship continues throughout childhood and often into the early to mid teen years.

Another tickling social relationship is that which forms between siblings of relatively the same age. [14] Many case studies have indicated that siblings often use tickling as an alternative to outright violence when attempting to either punish or intimidate one another. The sibling tickling relationship can occasionally develop into an anti-social situation, or tickle torture, where one sibling will tickle the other without mercy. The motivation behind tickle torture is often to portray the sense of domination the tickler has over the victim. [14]

As with parents and siblings, tickling serves as a bonding mechanism between friends, and is classified by psychologists as part of the fifth and highest grade of social play which involves special intimacy or "cognitive interaction". [14] This suggests that tickling works best when all the parties involved feel comfortable with the situation and one another. [15] It can also serve as an outlet for sexual energy during adolescence, [16] and a number of people have stated in a study that their private areas were ticklish. [17] [18]

While many people assume that other people enjoy tickling, a recent survey of 84 college students indicated that only 32% of respondents enjoy being tickled, with 32% giving neutral responses and 36% stating that they do not enjoy being tickled. [19] The study also found a very high level of embarrassment and anxiety associated with tickling. However, in the same study the authors found that the facial indicators of happiness and amusement do not correlate, with some people who indicated that they do not enjoy being tickled actually smiling more often during tickling than those who indicated that they do enjoy being tickled, [19] which suggests that there may be other factors at play (such as embarrassment and anxiety) in the case of those who indicated a dislike for tickling than the mere physical sensation experienced. It has also been suggested that people may enjoy tickling because it elicits laughter as well as the feeling of being tickled. Social psychologists find that mimicking expressions generally cause people to some degree experience that emotion. [9]

Excessive tickling has been described as a primary sexual obsession and, under these circumstances, is sometimes considered a form of paraphilia. [20] Tickling can also be a form of sexual harassment. [15]


Some of history's greatest thinkers have pondered the mysteries of the tickle response, including Plato, Francis Bacon, Galileo Galilei and Charles Darwin. [9] In The Assayer , Galileo philosophically examines tickling in the context of how we perceive reality: [21]

When touched upon the soles of the feet, for example, it feels in addition to the common sensation of touch a sensation on which we have imposed a special name, "tickling." This sensation belongs to us and not to the hand... A piece of paper or a feather drawn lightly over any part of our bodies performs intrinsically the same operations of moving and touching, but by touching the eye, the nose, or the upper lip it excites in us an almost intolerable titillation, even though elsewhere it is scarcely felt. This titillation belongs entirely to us and not to the feather; if the live and sensitive body were removed it would remain no more than a mere word.

Francis Bacon and Charles Darwin believed that humorous laughter requires a "light" frame of mind. But they differed on ticklish laughter: Darwin thought that the same light state of mind was required, whereas Bacon disagreed. When tickled, noted Bacon, "men even in a grieved state of mind, yet cannot sometimes forbear laughing." [22]

One hypothesis, as mentioned above, is that tickling serves as a pleasant bonding experience between parent and child. [9] However, this hypothesis does not adequately explain why many children and adults find tickling to be an unpleasant experience. Another view maintained is that tickling develops as a prenatal response and that the development of sensitive areas on the fetus helps to orient the fetus into favourable positions while in the womb. [23]

It is unknown why certain people find areas of the body to be more ticklish than others; additionally, studies have shown that there is no significant difference in ticklishness among the genders. [24] In 1924, J. C. Gregory proposed that the most ticklish places on the body were also those areas that were the most vulnerable during hand-to-hand combat. He posited that ticklishness might confer an evolutionary advantage by enticing the individual to protect these areas. Consistent with this idea, University of Iowa psychiatrist Donald W. Black observed that most ticklish spots are found in the same places as the protective reflexes. [25]

A third, hybrid hypothesis, has suggested that tickling encourages the development of combat skills. [9] Most tickling is done by parents, siblings and friends and is often a type of rough-and-tumble play, during which time children often develop defensive and combat moves. Although people generally make movements to get away from, and report disliking, being tickled, laughter encourages the tickler to continue. If the facial expressions induced by tickle were less pleasant the tickler would be less likely to continue, thus diminishing the frequency of these combat lessons.

To understand how much of the tickle response is dependent on the interpersonal relationship of the parties involved, Christenfeld and Harris presented subjects with a "mechanical tickle machine". They found that the subjects laughed just as much when they believed they were being tickled by a machine as when they thought they were being tickled by a person. [26] Harris goes on to suggest that the tickle response is reflex, similar to the startle reflex, that is contingent upon the element of surprise. [9]

Recently it was possible to show that it can be assumed that tickling (by passing leaves) served as a triggering-mechanism to issue an acoustic signal (namely laughing) to avoid crashes when our ancestors moved through tree tops. After our descent from the trees only body-parts remained ticklish that could not be touched by passing leaves (arm pits, sole of our feet etc.). It is also possible to show the further development of this trait which finally led to the upcoming of humor. [27]


The question as to why a person could not tickle themselves was raised by the Greek philosopher Aristotle. [9]

Knismesis may represent a vestige of the primitive grooming response, in effect; knismesis serves as a "non-self detector" and protects the subject against foreign objects. Perhaps due to the importance of knismesis in protection, this type of light touch is not dependent on the element of surprise and it is possible for one to induce self-knismesis, by light touching. [18]

Gargalesis, on the other hand, produces an odd phenomenon: when a person touches "ticklish" parts on their own body no tickling sensation is experienced. It is thought that the tickling requires a certain amount of surprise, and because tickling oneself produces no unexpected motion on the skin, the response is not activated. [18] In 1998, Blakemore and colleagues analyzed the "self-tickle" response by using MRI technology to investigate how the brain distinguishes between sensations we create for ourselves and sensations others create for us. When subjects used a joystick to control a "tickling robot", they could not make themselves laugh. This suggests that when a person tries to tickle himself or herself, the cerebellum sends to the somatosensory cortex precise information on the position of the tickling target and therefore what sensation to expect. Apparently an unknown cortical mechanism then decreases or inhibits the tickling sensation. [28]

While the reasons for the inhibition of the tickling sensation during self-tickling remain unknown, research shows that the human brain is trained to know what sensation to expect when the body moves or performs an action. [29] Another reason may be the lack of awareness of many sensations arising from self-movement, such as not paying attention to one's own vocal cords. When we try to tickle ourselves by grabbing our sides, the brain foresees this contact between body and hand and prepares itself for it. This removes the feeling of unease and panic, causing the body to not react to tickling in the same way it would if someone else supplied the stimulus.

However, some people with schizophrenia have the ability to tickle themselves. This is most likely largely due to the difficulty many people with the disorder have recognising their own actions. [30]

As physical abuse

Although some consensual tickling can be a positive, playful experience, non-consensual tickling can be frightening, uncomfortable, and painful for the recipient. Heinz Heger, a man imprisoned in the Flossenbürg concentration camp during World War II, witnessed Nazi prison guards perform tickle torture on a fellow inmate. He describes this incident in his book The Men with the Pink Triangle: [31] "The first game that the SS sergeant and his men played was to tickle their victim with goose feathers, on the soles of his feet, between his legs, in the armpits, and on other parts of his naked body. At first the prisoner forced himself to keep silent, while his eyes twitched in fear and torment from one SS man to the other. Then he could not restrain himself and finally he broke out in a high-pitched laughter that very soon turned into a cry of pain, while the tears ran down his face, and his body twisted against his chains. After this tickling torture, they let the lad hang there for a little, while a flood of tears ran down his cheeks and he cried and sobbed uncontrollably."

An article in the British Medical Journal describes a European method of tickle torture in which a goat was compelled to lick the victim's feet after they had been dipped in salt water. Once the goat had licked the salt off, the victim's feet would be dipped in the salt water again and the process would repeat itself. [32] In ancient Japan, authority figures could administer punishments to those convicted of crimes that were beyond the criminal code. This was called shikei, which translates as ‘private punishment’. One such torture was kusuguri-zeme: "merciless tickling." [33]

In his book Sibling Abuse, Vernon Wiehe published his research findings regarding 150 adults who were abused by their siblings during childhood. Several reported tickling as a type of physical abuse they experienced, and based on these reports it was revealed that abusive tickling is capable of provoking extreme physiological reactions in the victim, such as vomiting, incontinence (losing control of bladder), and loss of consciousness due to inability to breathe. [34]

See also

Further reading

Related Research Articles

Pain Type of unpleasant feeling

Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." In medical diagnosis, pain is regarded as a symptom of an underlying condition.

Laughter Expression of amusement

Laughter is a physical reaction in humans consisting usually of rhythmical, often audible contractions of the diaphragm and other parts of the respiratory system resulting most commonly in forms of "hee-hee" or "ha-ha". It is a response to certain external or internal stimuli. Laughter can arise from such activities as being tickled, or from humorous stories or thoughts. Most commonly, it is considered an auditory expression of a number of positive emotional states, such as joy, mirth, happiness, relief, etc. On some occasions, however, it may be caused by contrary emotional states such as embarrassment, surprise, or confusion such as nervous laughter or courtesy laugh. Age, gender, education, language, and culture are all indicators as to whether a person will experience laughter in a given situation. Some other species of primate show laughter-like vocalizations in response to physical contact such as wrestling, play chasing or tickling.

Erogenous zone Area of heightened sensitivity of the body, touching which may elicit a sexual response

An erogenous zone is an area of the human body that has heightened sensitivity, the stimulation of which may generate a sexual response, such as relaxation, sexual fantasies, sexual arousal and orgasm.

Itch Sensation that causes the desire or reflex to scratch

Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to be classified as any one type of sensory experience. Itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itch leads to a scratch reflex.

Stimulus (physiology)

In physiology, a stimulus is a detectable change in the physical or chemical structure of an organism's internal or external environment. The ability of an organism or organ to detect external stimuli, so that an appropriate reaction can be made, is called sensitivity. Sensory receptors can receive information from outside the body, as in touch receptors found in the skin or light receptors in the eye, as well as from inside the body, as in chemoreceptors and mechanoreceptors. When a stimulus is detected by a sensory receptor, it can elicit a reflex via stimulus transduction. An internal stimulus is often the first component of a homeostatic control system. External stimuli are capable of producing systemic responses throughout the body, as in the fight-or-flight response. In order for a stimulus to be detected with high probability, its level of strength must exceed the absolute threshold; if a signal does reach threshold, the information is transmitted to the central nervous system (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.

A mechanoreceptor, also called mechanoceptor, is a sensory cell that responds to mechanical pressure or distortion. There are four main types of mechanoreceptors in glabrous, or hairless, mammalian skin: lamellar corpuscles, tactile corpuscles, Merkel nerve endings, and bulbous corpuscles. There are also mechanoreceptors in hairy skin, and the hair cells in the receptors of primates like rhesus monkeys and other mammals are similar to those of humans and also studied even in early 20th century anatomically and neurophysiologically.


A nociceptor is a sensory neuron that responds to damaging or potentially damaging stimuli by sending “possible threat” signals to the spinal cord and the brain. If the brain perceives the threat as credible, it creates the sensation of pain to direct attention to the body part, so the threat can hopefully be mitigated; this process is called nociception.

Goose bumps

Goose bumps or goosebumps are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold or experiencing strong emotions such as fear, euphoria or sexual arousal.

Tickle torture is the use of tickling to abuse, dominate, harass, humiliate, or interrogate an individual. While laughter is popularly thought of as a pleasure response, in tickle torture, the one being tickled may laugh whether or not they find the experience pleasant. In a tickling situation, laughter can indicate a panic reflex rather than a pleasure response. Tickle torture may be a consensual activity or one that is forced, depending on the circumstances. In a consensual form, tickle torture may be part of a mutually fulfilling, physically-intimate act between partners. However, forced tickle torture can cause real physical and mental distress in a victim, which is why it has been used as an interrogation method or to simply show dominance over another person.

Sensory overload

Sensory overload occurs when one or more of the body's senses experiences over-stimulation from the environment. There are many environmental elements that affect an individual. Examples of these elements are urbanization, crowding, noise, mass media, technology, and the explosive growth of information.

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.

Tickling game Interpersonal or social activities

Tickling games are interpersonal or social activities involving the tickling of one person by another. Some people find tickling to not only be a pleasurable experience, but also an erotic one. They may be sexually excited by being tickled or by tickling another person, some people like being tickled on their genitals, their waist, their feet, their underarms, their anus or their breasts while others prefer to tickle and some like doing both. Some engage in tickling games as part of a social act.

Group C nerve fiber

Group C nerve fibers are one of three classes of nerve fiber in the central nervous system (CNS) and peripheral nervous system (PNS). The C group fibers are unmyelinated and have a small diameter and low conduction velocity, whereas Groups A and B are myelinated. Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots. These fibers carry sensory information.

Tactile discrimination is the ability to differentiate information through the sense of touch. The somatosensory system is the nervous system pathway that is responsible for this essential survival ability used in adaptation. There are various types of tactile discrimination. One of the most well known and most researched is two-point discrimination, the ability to differentiate between two different tactile stimuli which are relatively close together. Other types of discrimination like graphesthesia and spatial discrimination also exist but are not as extensively researched. Tactile discrimination is something that can be either more or less severe in different people and two major conditions, chronic pain and blindness, can affect it greatly. Blindness increases tactile discrimination abilities which is extremely helpful for tasks like reading braille. In contrast, chronic pain conditions, like arthritis, decrease a person's tactile discrimination. One other major application of tactile discrimination is in new prosthetics and robotics which attempt to mimic the abilities of the human hand. In this case tactile sensors function similarly to mechanoreceptors in a human hand to differentiate tactile stimuli.

Hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy (HSN) is a condition used to describe any of the types of this disease which inhibit sensation.

Somatosensory system Widely distributed parts of the sensory nervous system

The somatosensory system is a part of the sensory nervous system. The somatosensory system is a complex system of sensory neurons and neural pathways that responds to changes at the surface or inside the body. The axons of sensory neurons connect with, or respond to, various receptor cells. These sensory receptor cells are activated by different stimuli such as heat and nociception, giving a functional name to the responding sensory neuron, such as a thermoreceptor which carries information about temperature changes. Other types include mechanoreceptors, chemoreceptors, and nociceptors which send signals along a sensory nerve to the spinal cord where they may be processed by other sensory neurons and then relayed to the brain for further processing. Sensory receptors are found all over the body including the skin, epithelial tissues, muscles, bones and joints, internal organs, and the cardiovascular system.

Laughter in animals

Laughter in animals other than humans describes animal behavior which resembles human laughter.

Sensation is the physical process during which sensory systems respond to stimuli and provide data for perception. A sense is any of the systems involved in sensation. During sensation, sense organs engage in stimulus collection and transduction. Sensation is often differentiated from the related and dependent concept of perception, which processes and integrates sensory information in order to give meaning to and understand detected stimuli, giving rise to subjective perceptual experience, or qualia. Sensation and perception are central to and precede almost all aspects of cognition, behavior and thought.

As long as humans have experienced pain, they have given explanations for its existence and sought soothing agents to dull or cease the painful sensation. Archaeologists have uncovered clay tablets dating back as far as 5,000 BC which reference the cultivation and use of the opium poppy to bring joy and cease pain. In 800 BC, the Greek writer Homer wrote in his epic, The Odyssey, of Telemachus, a man who used opium to soothe his pain and forget his worries. While some cultures researched analgesics and allowed or encouraged their use, others perceived pain to be a necessary, integral sensation. Physicians of the 19th century used pain as a diagnostic tool, theorizing that a greater amount of personally perceived pain was correlated to a greater internal vitality, and as a treatment in and of itself, inflicting pain on their patients to rid the patient of evil and unbalanced humors. This article focuses both on the history of how pain has been perceived across time and culture, but also how malleable an individual's perception of pain can be due to factors like situation, their visual perception of the pain, and previous history with pain.

Mirror-touch synesthesia is a rare condition which causes individuals to experience a similar sensation in the same part or opposite part of the body that another person feels. For example, if someone with this condition were to observe someone touching their cheek, they would feel the same sensation on their own cheek. Synesthesia, in general, is described as a condition in which a stimulus causes an individual to experience an additional sensation. Synesthesia is usually a developmental condition; however, recent research has shown that mirror touch synesthesia can be acquired after sensory loss following amputation.


  1. 1 2 "Tickling". Dictionary.com. Retrieved 2012-05-27.
  2. Hall, G. S., and A. Allin. 1897. The psychology of tickling, laughing and the comic. The American Journal of Psychology 9:1-42.
  3. 1 2 Selden, S. T. (2004). "Tickle". Journal of the American Academy of Dermatology. 50 (1): 93–97. doi:10.1016/s0190-9622(03)02737-3. PMID   14699372.
  4. Panksepp J, Burgdorf J (2003). ""Laughing" rats and the evolutionary antecedents of human joy?" (PDF). Physiol. Behav. 79 (3): 533–47. doi:10.1016/S0031-9384(03)00159-8. PMID   12954448. S2CID   14063615.
  5. "The Psychology of Tickling And Why It Makes Us Laugh". Big Think. 12 July 2016.
  6. Zotterman Y (1939). "Touch, pain and tickling: An electrophysiological investigation on cutaneous sensory nerves". Journal of Physiology. 95 (1): 1–28. doi:10.1113/jphysiol.1939.sp003707. PMC   1393960 . PMID   16995068.
  7. Lahuerta J, et al. (1990). "Clinical and instrumental evaluation of sensory function before and after percutaneous anterolateral cordotomy at cervical level in man". Pain. 42 (1): 23–30. doi:10.1016/0304-3959(90)91087-Y. PMID   1700355. S2CID   24785416.
  8. Nathan PW (1990). "Touch and surgical division of the anterior quadrant of the spinal cord". J. Neurol. Neurosurg. Psychiatry. 53 (11): 935–9. doi:10.1136/jnnp.53.11.935. PMC   488271 . PMID   2283523.
  9. 1 2 3 4 5 6 7 8 Harris, Christine R. (1999). "The mystery of ticklish laughter". American Scientist. 87 (4): 344. Bibcode:1999AmSci..87..344H. doi:10.1511/1999.4.344.
  10. Bakos, Susan (2008). The Sex Bible: The Complete Guide to Sexual Love. Minneanapolis: Quiver. p. 256. ISBN   978-1-59233-285-4.
  11. Newman B, O'Grady MA, Ryan CS, Hemmes NS (1993). "Pavlovian conditioning of the tickle response of human subjects: Temporal and delay conditioning". Perceptual and Motor Skills. 77 (3 Pt 1): 779–85. doi:10.2466/pms.1993.77.3.779. PMID   8284153. S2CID   38446310.
  12. Darwin, C. 1872/1965. The Expressions of the Emotions in Man and Animals. London: John Murray.
  13. Loftis, Fridlund; Jennifer (April 1990). "Alan". Relations Between Tickling and Humorous Laughter: Preliminary Support for the Darwin-Hecker Hypothesis. Biological Psychology. 30 (141–150): 201.
  14. 1 2 3 4 5 Fagen R. The Future of Play Theory: A Multidisciplinary Inquiry into the Contributions of Brian Sutton-Smith . Albany NY: SUNY Press; 1995. p. 22–24.
  15. 1 2 Michael Moran, Erotic Tickling, Greenery Press, 2003. ISBN   1-890159-46-8.
  16. Freud S. "Three contributions to the theory of sex." In: The Basic Writings of Freud. New York: Modern Library; 1938.
  17. "The surprising reasons why we tickle one another". The Washington Post. 6 February 2016.
  18. 1 2 3 Selden ST (2004). "Tickle". J. Am. Acad. Dermatol. 50 (1): 93–7. doi:10.1016/S0190-9622(03)02737-3. PMID   14699372.
  19. 1 2 Harris C.R. and Nancy Alvarado. 2005. "Facial expressions, smile types and self-reporting during humour, tickle and pain" (pdf) Archived 2006-09-23 at the Wayback Machine Cognition and Emotion. 9(5),655-669.
  20. Ellis H. Studies in the psychology of sex. Vol iii. Philadelphia: FA Davis Co.; 1926.
  21. Drake, Stillman (1957). "Discoveries and Opinions of Galileo". New York: Doubleday & Co. p. 275. Retrieved 2008-11-10.
  22. Darwin, C. 1872/1965. The Expressions of the Emotions in Man and Animals. London: John Murray.
  23. Simpson JY. On the attitude of the fetus in utero. Obstetric Memoirs, vol ii. Philadelphia: Lippincott; 1855-1856.
  24. Weinstein, S. 1968. Intensive and extensive aspects of tactile sensitivity as a function of body part, sex, and laterality. In The Skin Senses, ed. D. R. Kenshalo. Springfield, Ill.: Thomas. pp. 195-222.
  25. Black DW (1984). "Laughter". JAMA. 252 (21): 2995–8. doi:10.1001/jama.252.21.2995. PMID   6502861.
  26. Harris, C. R., and N. Christenfeld. In press. Can a machine tickle? Psychonomic Bulletin and Review.
  27. Dramlitsch, T., 2018: "The Origin of Humor", ISBN   978-1720264637
  28. Blakemore SJ, Wolpert DM, Frith CD (1998). "Central cancellation of self-produced tickle sensation". Nat. Neurosci. 1 (7): 635–40. doi:10.1038/2870. PMID   10196573. S2CID   9260106.
  29. "Tickling, on season 11, episode 5". Scientific American Frontiers . Chedd-Angier Production Company. 2000–2001. PBS. Archived from the original on 2006.
  30. Lametti, Daniel (21 December 2010). "Can't Tickle Yourself? That's a Good Thing". Scientific American . Retrieved 8 February 2012.
  31. Heger, Heinz. The Men With the Pink Triangle. Boston: Alyson Publications, 1980.
  32. Yamey, Gavin (2001). "Torture: European Instruments of Torture and Capital Punishment from the Middle Ages to present". British Medical Journal. 323 (7308): 346. doi:10.1136/bmj.323.7308.346. PMC   1120948 .
  33. Schreiber, Mark. The Dark Side: Infamous Japanese Crimes and Criminals. Japan: Kodansha International, 2001. Page 71.
  34. Wiehe, Vernon. Sibling Abuse: Hidden Physical, Emotional, and Sexual Trauma. New York: Lexington Books, 1990.