"I Love to Laugh", also called "We Love to Laugh", is a song from Walt Disney's film Mary Poppins. It was composed by Richard M. Sherman and Robert B. Sherman. The song is sung in the film by "Uncle Albert" (Ed Wynn), and "Bert" (Dick Van Dyke) as they levitate uncontrollably toward the ceiling, eventually joined by Mary Poppins (Julie Andrews) herself. The premise of the scene, that laughter and happiness cause Uncle Albert (and like-minded visitors) to float into the air, can be seen as a metaphor for the way laughter can "lighten" a mood. (Compare Peter Pan's flight power, which is also powered by happy thoughts.) Conversely, thinking of something sad literally brings Albert and his visitors "down to earth" again. The song states a case strongly in favor of laughter, even if Mary Poppins appears to disapprove of Uncle Albert's behavior, especially since it not only complicates the task of getting Albert down, but the infectious mood sends Bert and the Banks children into the air as well.
The scene is based on the chapter "Laughing Gas" in the book Mary Poppins by P.L. Travers. In the book, Mary's Uncle Albert, also called Mr. Wigg, is said to float because of an excess of "laughing gas", although it is clear that the term is not used in the chemical sense. So-called "laughing gas" (nitrous oxide) was one of the earliest effective anaesthetics developed in the Nineteenth century. it was popularised by dentists, for pain-free tooth extractions, as well as by showground novelty booths. Customers at the booth would be gassed and, as they were recovering from the drugged sleep they often felt euphoric and giggly. Hence the name. A famous 1931 British comedy sketch starring Cicely Courtneidge, called "Laughing Gas", was based on this idea. A group of people meet, very seriously, to hear the reading of a will. However a large bottle of laughing gas has been placed just off-stage, and begins to leak. As the will is read, the listeners become increasingly hysterical, despite the obvious seriousness of the death-related situation, with obvious comic effects.