When the good people of Maycomb sang, it was often about the Lord. Here is a collection of hymns that Scout and Jem would have been forced to sing in church, either their own or Calpurnia's.
It was one of Scout's favorites, and children are still singing it at schools today. Get out your recorders for a rousing good time. Hee haw!
Okay, we have no direct evidence that Harper Lee is a Coen Brothers' fan. But the soundtrack to their film is a haunting collection of songs that would have been sung by people, both black and white, in 1930s Alabama.