The melody comes from Jim Knopf und Lukas der Lokomotivführer, Michael Ende's story about a boy living on Lummerland, a tiny island with two mountains. The Augsburger Puppenkiste puppet series made the tune famous across Germany in the early 1960s, and generations have since sung it from memory. Short clips now circulate online as a shorthand for nostalgia, innocence and small, cosy worlds, which is why creators still reach for just a few seconds of it.