It helps that John is obviously having a hard time keeping a straight face, for all his efforts otherwise. It helps also that yes, John is obviously hamming it up. Ianto's eyebrows shoot up again at the chorus and yes, that's definitely the twitch of a smile that John's rewarded in return. He doesn't miss that this is probably for his benefit, and feels a little ridiculous for needing to be coddled so, but he appreciates the gesture either way.

He waits until John's settled down from the chorus into another vamp on the guitar before he comments, "Flying flaming cows." What kind of a song is this that you're playing for him, John? For that matter, how mournful is 'Yippie yi oh' supposed to sound anyway?