Buddy Ebsen sings

If you listen closely, during the singing of "We're Off To See The Wizard" by Dorothy, the Scarecrow and the Tin Man, you can recognise Buddy Ebsen's gravelly voice. He was the original Tin Man, but had a reaction to the makeup. They had already recorded the songs and it was too expensive to re-do it. (This film was WAY over budget and they couldn't waste time and money re-recording songs)