The laugh- and/or smile-evoking potency of laughter was evaluated by observing responses of 128 subjects in three undergraduate psychology classes to laugh stimuli produced by a “laugh box.” Subjects recorded whether they laughed and/or smiled during each of 10 trials, each of which consisted of an 18-sec sample of laughter, followed by 42 sec of silence. Most subjects laughed and smiled in response to the first presentation of laughter. However, the polarity of the response changed quickly. By the 10th trial, (...) few subjects laughed and/or smiled, and most found the stimulus “obnoxious.” Although other research has described canned-laughter effects, it did not consider the hypothesis confirmed here, that laughter itself evokes laughter, perhaps by activating a laughter-specific auditory-feature detector. This result is relevant to the neurological basis of social communication, human ethology, and theories of speech production and perception. (shrink)