Directed by animator Norm Fergusen, "Pink Elephants On Parade" is one of the most famous sequences from the animated feature Dumbo (1941). Halfway through the movie, Dumbo the baby elephant and Timothy Mouse drink from a bucket of water that, unbeknownst to them, has been spiked with alcohol. In their drunken state, they're confronted with nightmarish illusions of pink elephants, which dance, contort, and convert into a myriad of forms to the sinister song "Pink Elephants On Parade," by Disney veteran songwriters Oliver Wallace and Ned Washington.
"Pink Elephants On Parade" is unusual for an early Disney feature segment in that it blatantly breaks the "fourth wall," or the boundary between fiction and the audience -- first via the elephants marching around the perimeter of the movie screen; and then via the song itself through the lyrics about "Technicolor pachyderms" (Technicolor being the color film process used by Disney). Disney cartoon shorts regularly broke the fourth wall, but the early features were generally off limits for this treatment (though the wisecracking Jiminy Cricket does flirt with speaking directly to the film audience through his narration and commentary in Pinocchio, 1940).
Disney studio artists have tried many times since to recapture the wild invention of "Pink Elephants on Parade." Notable attempts include "Heffalumps and Woozles" from Winnie the Pooh and the Blustery Day, 1968, and the Genie in Aladdin, 1992.
A bit of trivia: The term "pink elephants" as a reference to drunkenness is generally attributed to (or blamed on) author Jack London. He's credited with the first usage of the term, in his novel John Barleycorn (1913): "There are, broadly speaking, two types of drinkers. There is the man whom we all know, stupid, unimaginative, whose brain is bitten numbly by numb maggots; who walks generously with wide-spread, tentative legs, falls frequently in the gutter, and who sees, in the extremity of his ecstasy, blue mice and pink elephants. He is the type that gives rise to the jokes in the funny papers."