This article contains details of the ending and/or a surprise plot element.
Betty Boop is a character created by Max Fleischer who is recognized as one of the most iconic cartoon characters of all time. Her cartoons were designed for adult audiences, making her the first animated sex symbol, as a good deal of the cartoon shorts contained some risque material.
Kitty From Kansas City
Though Kitty was not supposed to be Betty Boop but an identical lookalike (at its time of release, 1931, Betty was a dog), it still counts today as a Betty Boop cartoon as it has appeared on some Betty Boop DVDs. Kitty is a portly, simple-minded character whose weight is clearer to see after Rudy Vallée's live-action performance of the song. ("I hope she doesn't get much fatter but if she does that doesn't matter")
When the song is over, she rides her horse but sits the wrong way, so she commands him to go the way she's facing until the horse is too skinny to go any further. They swap positions but swap weights, as the horse ends up as fat as Kitty was. They revert to their normal positions and proceed until Kitty falls off a cliff into the water.
Betty Boop, M.D.
Betty, along with Bimbo and Koko the Clown, is hosting a medicine show going on tour. One of their patients is a man who is too thin, so Betty gives him medicine that makes him fat enough to make him happy. As he walks away, he stops so that Betty sticks a "Detour" sign on his backside.
Betty Boop and Little Jimmy
In this crossover short starring Betty Boop and newspaper strip star Little Jimmy, the two are exercising as Betty sings about it. Jimmy ends the song by saying, "If you're thin, don't worry over that. Just begin to laugh and you'll grow fat". When Betty's exercise machine gets stuck, Jimmy fixes it leaving Betty Boop skinnier than she hoped and looking so funny that the two begin to laugh so hard they grow very fat. They reprise Jimmy's verse and continue to laugh, growing fatter and fatter.