"Perhaps not essential, but if you address me in French, I am going to be curious as to what you say." Watson peered at him over the top of his coffee, one raised eyebrow. He was finding this playing about in French to be faintly annoying, honestly, but at the same time... it was so very Holmes, and he loved it, even if he didn't understand more than the odd word. "Particularly when it drops down into an otherwise uneventful conversation like that. Call a greivous character flaw, if you must."