The easiest and hardest feature to write

Of all the recurring features on this blog, the persistent earworm alerts are the easiest--and hardest--to write.  Half the battle is won just by writing, "This song has been running through my mind."  Elaborating on why the song is lodged so firmly in my brain or why the song is compelling or grating is the challenging part, however.  It's not enough to say, "Wow, this song is on my mind.  I wonder why."