It also seems like something that would translate well to piano. There's more plucking than strumming, not very many chords to work out, just lots of notes in sequence to work out, with some slight dual-note harmonizing. B listens close, and thinks he can maybe even do it.

He's so busy focusing on the notes he couldn't even really tell you if it was a nice song or not. What he can say is, "You're good." Not a single mis-plucked note, as far as he can tell.