An interior convulsion, producing a distortion of the features and accompanied by inarticulate noises. It is infectious and, though intermittent, incurable. Liability to attacks of laughter is one of the characteristics distinguishing man from the animals -- these being not only inaccessible to the provocation of his example, but impregnable to the microbes having original jurisdiction in bestowal of the disease. Whether laughter could be imparted to animals by inoculation from the human patient is a question that has not been answered by experimentation. Dr. Meir Witchell holds that the infection character of laughter is due to the instantaneous fermentation of _sputa_ diffused in a spray. From this peculiarity he names the disorder _Convulsio spargens_.
A movement (usually involuntary) of the muscles of the face, particularly of the lips, with a peculiar expression of the eyes, indicating merriment, satisfaction, or derision, and usually attended by a sonorous and interrupted expulsion of air from the lungs. See Laugh, v. i.
the activity of laughing; the manifestation of joy or mirth of scorn; "he enjoyed the laughter of the crowd"
To express certain emotions, especially mirth, delight, or derision, by a series of spontaneous, usually unarticulated sounds often accompanied by corresponding facial and bodily movements. A person with Alzheimer's or dementia does not lose this ability , but their sense of humor may change with the progression of the disease.