I only came across the word “earworm” recently; and discovered that I am not the last person in the world to find out what an earworm is. My current earworm is the Faure song “En Priere” with its haunting melody and adroit modulations.
To my amazement, there is a whole Wikipedia article about earworms:
Earworms have provided the starting point for a number of ingenious literary plots. I wonder if you could compose a musical piece based on an earworm? Or has that already been done? (Pachelbel’s Canon comes to mind…)