[John chuckles at the joke, but goes quiet once Sherlock starts to play. He's definitely not able to tell that Sherlock is unfamiliar with the song; it sounds excellent to him. He lets Sherlock finish the song before he continues speaking.]

That was fantastic. We'll have the most musical snake of all, mark my words. I'd consider joining in with my clarinet, but I'm so out of practice it'd probably sabotage these pre-hatching music lessons.