That was the harmonica song that he taught Emma. Other than Emma and him, not a second one knew of this tune throughout all these years. After Emma became missing, during his toughest and darkest days, he had played it thrice. However, for those three times, he was alone in the depths of hell. No one was around him. This rearranged harmonica song was very tough to play.
The leaps between the musical notes were very big. Without a musical foundation, it would be hard to learn it. Emma had a tough time learning it that year. The first time she played the harmonica, she was quite bad. However, she put in a lot of effort and was very talented. After learning for a few days, she was quite adept at it. After her, he did not teach any other person.