“Heartwarming and counts as a Crowning Moment of Acting on both sides- at the beginning of A Study in Pink, both Sherlock and John seem absolutely incapable of actually, genuinely smiling. John’s been through a lot, is depressed, and hasn’t got a lot of reason to. Sherlock does try to smile on occasion, with hilarious results (he seems to think ‘move lips outward at both ends briefly but enthusiastically’ is the definition of ‘smile.’ You can really see it after he tells John “prospective housemates should know the worst about each other” and it crops up in other places where Sherlock evidently feels a smile is in order. It’s awkward as hell.) In any case, the ice-breaking conversation at the restaurant and the chase after the cab are a watershed of sorts for both of them. They laugh about “welcome to London”, and by the time they arrive back at Baker Street they’re both giggling like loons, which is hilarious and adorable.”