The Locomotive Manipulation - S7-E15
Continuity mistake: At the end of the episode when Lennard asks Sheldon about his train ride, he says that he kissed Amy on the lips, and says that it tasted like the brownies that they had that for dessert. But they were eating a tart of some type, with a shortbread crust. No brownies were on the table.
Chosen answer: The song is called "Dark as a Dungeon" and was written and first performed by singer-songwriter Merle Travis in 1946. It has been performed by a wide array of artists, including Tennessee Ernie Ford, Harry Belafonte, Dolly Parton, Queens of the Stone Age, Kathy Mattea and Amy Grant. But it was made most famous when it was performed and recorded by Johnny Cash during his concert at Folsom Prison in 1968. According to Wikipedia: "It is a lament about the danger and drudgery of being a coal miner in an Appalachian shaft mine. It has become a rallying song among miners seeking improved working conditions."
Michael Albert