Polly Put the Kettle On isn't usually in a modal key, but this week's Tune of the Week appears to be in Gm. If I knew more, I could confirm the scale is G aeolian. To play it the most easily I used cello banjo and brought the notes down four steps, so that's even more complex. I suppose this is all a good cognitive exercise to keep my brain a bit spry, which it needs.