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Remote Ready Biology Learning Activities has 50 remote-ready activities, which work for either your classroom or remote teaching.
Synesthesia
I think that you bring up an interesting point, Kathy. Have you ever thought that maybe you remember songs because of the presence of other sensory information? Perhaps you recognize a similar place or person and think of the song. This reminded me of something I learned about in another neurobiology course. Synesthesia is a condition where someone associates inputs from multiple senses. For example, a person might think of the color red when they hear the number 6, or something crazy like that. This website explains it a lot better than I could: http://faculty.washington.edu/chudler/syne.html.
Maybe the association between spontaneously recalling songs and synesthesia is way off base. But maybe you think of a song or certain song lyrics because you're reminded of it by being in a certain state of mind, or by being near someone who reminds you of the song in some way. Perhaps there are other senses at play when you remember a song (seemingly) randomly.