It’s times like this I wish the comic was musically scored.
For your information, Caryn and the Juilliard-trained pianist are playing the brief but intense songlet “Foreplay”, now made famous by the game Rock Band, which by the way is totally badass. (It should be noted that I judge badassitude by how much something sounds like the boss music in Final Fantasy 7. That’s why I like Deep Purple so much.) Caryn is playing the difficult and awesome bass part, so Jeria’s dismissal of her musical talent seems baseless, although maybe she is playing it badly. Also, wasn’t that a guitar before? Maybe she has a heart-shaped guitar AND a heart-shaped bass.
As for the musical punchline, although it’s admittedly hard to understand (like several of the lines in this strip in particular, it relies on a pristine memory of the “My Fair Lance and Eskimo” storyline), I am not going to explain it to you because it is just not worth it. You will figure it out and you will groan.