Oh come on, Ariane, it's obvious. They're in Paris, the city of love. They spent the night making love passionately. John was exhausted this morning, he preferred staying in bed and eating croissants in order to recover his strength for tonight. No, wait, for this afternoon. Just after Sherlock's lunch. When they make love passionately again. (Yes, I know this is not what I said to Anarion but I prefer this explanation actually. :D) Also, Sherlock stole a tiny skull from the Catacombs and he'll give it to John. (Because he's a romantic at heart.) When they're back in 221B he'll put it close to the other, on the mantelpiece, to keep it company, and he'll talk to it in French. Anarion, your story is so inspirational! :D