Liz challenged us to write a tune in Bb. I decided to avoid the trival route of just writing it on a Bb or F whistle. That meant I had to teach myself how to play in Bb on my C#/D accordion, which I did as I was writing the tune. I also chose low A as the second note so it wouldn't be natural to play on the Bb whistle. Other than that entire thing is built around what I found comfortable to play on C#/D.