Why has Robert Johnson got methane on his mind?
I was listening to The Complete Recordings earlier, and in the first of two versions of ‘Rambling On My Mind’ (though not in the second), he sings (I’m sure), “I got methane on my mind”.
You don’t want to dig too deeply into these things, though: they can spoil things.
I feel the need to quote Billy Bragg at this point: “The temptation/to take the precious things we have apart to see how they work/must be resisted for they never fit together again”. Not quite what he was talking about, but still.