The chain gang song at the begining "Po Lazarus" was a real chain gang singing from the 1950's recorded by a music historian. Amazing story:
In 1959, an amateur singer named James Carter was an inmate in camp B of the Mississippi State Penitentiary in Parchman, Mississippi. He and the others in his chain gang were chopping wood while singing when folk music historian Alan Lomax met them and decided to record the group.
Carter, credited as the soloist, and the rest of the chain gang, sang an old spiritual song, “Po’ Lazarus,” to the timing of their log cutting. The recording was purchased by the Coen Brothers for their film, which eventually went on to win a Grammy. The Coen Brothers decided to track down Carter, and he was paid $20,000.
I love redemption stories.