So there is a swing song in the Happy Potter and the Prisoner of Azkaban movie. It just plays on the background as Harry comes to Lupins office, hardly noticeable so you cannot put it into Shazam or something. I think it's quite famous song from the 20s-30s era but however I tried I couldn't google what it is.
Here is a youtube clip of that scene:
Does anyone know what song that is? Thank you!