The story involves the character Piggy, who picks up his girlfriend Fluffy and takes her to a theater where a hot jazz orchestra is playing. Piggy mocks the trumpet soloist, then crashes the stage to play a corny chorus of the 1873 hit "Silver Threads Among the Gold" on the saxophone. The audience, led by three shabbily-dressed drunken dogs in the balcony, mock Piggy with the title song "You Don't Know What You're Doin,'" as Piggy defends his self-perceived "talent."
One of the tipplers (a black dog, perhaps a prototype of Goopy Geer) joins Piggy onstage. The dog drinks from a bottle of bootleg hootch (the film was made during alcohol Prohibition in the USA), and belches in Piggy's face. The fumes on his breath instantly intoxicate Piggy. Piggy snatches the booze and runs out of the theater with the dog chasing him. He pours some of it into the radiator of an automobile, which arches its back like a frightened cat and takes Piggy for a wild ride through the city. Even the streets, lampposts, telephone poles, and background buildings seem to come to life in a loopy, drunken state.
The dog continues to chase after Piggy, but both of them eventually end up in the back of a truck which dumps them into a trash can. Both of them shout out "Whoopee!" as the cartoon comes to an end.
Which instrument does Piggy play on the stage?
Saxophone