Tickling, a kind of nonsexual sensation that is pleasurable at first, but that becomes painful when extreme. Tickling  causes laughter; taken too far it becomes unbearable; it can even be fatal, if some stories are to be believed.

This sensation must therefore consist in a stimulation of the organ of feeling, like the stimulation causing all pleasurable sensations, but which is still more acute, and even acute enough to arouse the spirit and the nerves strongly, and bring about agitation that is more violent than that usually accompanying pleasure; in this way the stimulation approaches the disturbances that cause pain.

The keen stimulation produced by tickling  comes, first, from the sensation caused by the object, as when we pass a feather lightly over our lips, and second, from the extremely sensitive disposition of our senses, that is, of the very many nerve-endings on the skin’s surface, which are highly prone to arousal, and which are charged with a good deal of spirit. This is why all ticklish people are very sensitive and alert, and why only the parts of the body with the most nerves can be tickled.

The organ can also be made more sensitive, as it needs to be for  tickling , by being slightly inflamed. That is why rubbing itches lightly brings so much pleasure. But this pleasure, as for  tickling,  is a near neighbour of pain.

As well as the dipositions of the object and the body, imagination also plays an important part in  tickling,  as it does in all other sensations.

If someone touches the less sensitive parts of our bodies with a determined air to tickle us, we cannot bear it; if, on the other hand, someone brings their hand near our skin without design, we do not feel any great impression, and we can touch the most ticklish parts of our bodies ourselves and feel quite unmoved. Surprise or defiance are therefore necessary to the dispositions of the organs and the object for tickling.

This mental feeling sends a large amount of spirit into the organs of feeling and the muscles joined to them; it brings them into play, thereby making the organs tenser, more sensitive, and the muscles ready to contract at the least impression. It is a kind of terror in the sense of feeling. See the articles Sensations, Pleasure [Pleasure (Ethics), Pleasure (Synonyms)], Pain, Nerve, Sympathy, Tact.