A camera pans across the continent of Africa where the narrator describes how dark and terrifying it is, amid jungle sounds and roars. As the camera pans across the darkest area, we hear the melodious sound of someone singing. A second later the camera opens on a singing giraffe named Nelly, who is performing for her animal friends. A hunter appears from out of the bush, and exclaims, "I wouldn't have believed it if I hadn't heard it with me own eyes!" and immediately has her sign a contract offering her fame and fortune.
Nelly waves a tearful goodbye to her friends in the jungle as she leaves for civilization, captivated by the idea of show business. Once she arrives in New York City, she is put to work singing jingles for "Algonquin Rutabaga Tonic" - a cure for ailments, puts on live stage shows, and produces a line of giraffe-neck sweaters (a play on "turtle-neck" sweaters). The camera closes in on a turtle reading a magazine article on the giraffe-neck clothing. He turns to the camera and says, "Well, that's show business".
Nelly releases several albums, but over time becomes lonely with fame and longs for male companionship. One day she wanders into the Zoo and falls in love with a male giraffe, but she finds out he's already married (albeit unhappily, as the "wife" catches him looking at her). Scandal ensues and her agent tells her she's ruining her career, and she leaves show business to be with her new love interest. Nelly returns to the Zoo and finds her guy snuggling with his wife. He turns to her and calls her a "has-been". Nelly is devastated, and contemplates suicide, as she knows her career is now over and she may never find true love again.
Next, we hear Nelly singing a beautiful love song as we see her sad reflection in a pond back in Africa, tears dripping from her eyes, and from the eyes of her jungle friends. Moments later, another male giraffe begins singing along with her. They meet, fall in love, everyone's happy, and the cartoon ends.
- Nominated for an Academy Award in 1962, for Best Short Subject, Cartoons.
- Ed Prentiss, the narrator of this film, used to be "Captain Midnight" on radio in the 1940s.
- Ed Prentiss also narrated Chuck Jones' "Martian Through Georgia" a year later.
- Gloria Wood sang the original "Rice-A-Roni, The San Francisco Treat" TV jingle.
- Gloria Wood was also the vocalist for Kay Kayser's "The Woody Woodpecker Song" and was dubbed the singing voice of Marilyn Monroe, Vera Ellen, and Betty Grable.
- Nelly's Folly did not end with the familiar "That's all, folks!" title card, but rather, with a slide that read: "Merrie Melodies: A Warner Bros. Cartoon. A Vitaphone Release". These words appeared in purple, green, and blue, respectively, against a black background.
- "Auld Lang Syne"
- "The Flower of Gower Gulch", written by Michael Maltese
- "Voices of Spring", by Johann Strauss
- "Aloha Oe", by Queen Liliuokalani
- "Columbia, Gem of the Ocean", aka "The Red, White and Blue"
- "Then You'll Remember Me", from Balfe's opera "The Bohemian Girl"