I apologize for this post, as you'd probably be spending the rest of your day humming this little ditty. Actually, it's not just any piece of music - it's the mother of all earworm.
The subject at hand is "It's a Small World (After All)," and the topic is why it's such an annoying song:
James J. Kellaris, a marketing professor at the University of Cincinnati, has done extensive research on what makes certain songs get stuck in the head. His theory is that music can create a "cognitive itch—the mental equivalent of an itchy back," especially when three qualities are present: repetition, musical simplicity, and incongruity.
No one would argue that "It's a Small World (After All)" isn't simple or repetitive. The word "world" appears 14 times in the 22 English lines of the song. Its verses are short, and the chorus consists of one line, repeated three times, followed by a slight variation on that line.
That lyrical repetition is reinforced by the song's insistent musical theme, which Robert B. Sherman's son, Robert Sherman Jr., broke down on Songfacts.com: "One thing which makes this song particularly 'catchy' is that the verse and chorus work in counterpoint to each other," he said. "This means that you can play the same chords over and over again, but with different melodies. The repetitive, yet varied pattern tricks your mind into absorbing the work without it becoming tiresome to your ear. There are many who would disagree with this, however!"
As for incongruity, one could point to the cheerful young singers of "It's a Small World (After All)." An online poll conducted by composer Dave Soldier in 1996 surveyed approximately 500 people about their most and least favorite musical sounds. Children's choirs were on the "hated" list, along with bagpipes, accordions, banjos, synthesizers, harps, and organs.