I find myself spending an inordinate amount of time watching supercuts of film tropes. Did you know there's a supercut of every "fuck" said in The Wolf of Wall Street? It's about five minutes long.
Sometimes I get a single phrase of a song stuck in my head for weeks on end. Right now it's, "...and you're standing here beside me; I love the passage of time," from This Must Be the Place by Talking Heads.