McGonagall’s athletic heritage
Fans of Harry Potter are rabid, and like any true fan, they can’t help but speculate about the unknown backstories of their favourite characters. We assume that’s why there’s fanfiction. Rowling, on the other hand, did an excellent job of slipping in a few tidbits here and there.
Most people probably missed this one, but as you can see, Professor McGonagall’s background was only mentioned briefly here. Although the focus is on Harry’s father, the fact that McGonagall was once an athlete is fascinating and amusing to speculate about.