申論題

 The amazing contagiousness of laughter works across species. At the primate center where I work, I often hear chimpanzees laugh when they tickle one another, and I cannot suppress a chuckle in response. Tickling must be the original context of laughter, and the fact that tickling oneself is notoriously ineffective confirms its social significance. Tickling and laughter are essentially play patterns, with the latter having achieved a considerably expanded meaning in our species.