Observing. Noticing every detail. Sherlock prides himself on his ability to put together a complete picture of someone based on little things that others would miss. He can tell you your life story after a cursory glance. But, the intricacies of human behaviour are not so clear to him. Oh, he knew Molly’s new dress and lipstick was for the benefit of someone she admired, but the revelation that someone was himself came as a complete shock.
And, now, when he thinks she’s going to bore him with a profession of sentiment, she points out a detail about himself that he thought he had hidden well. And, before he can respond, she walks away, leaving him wondering if this is how it feels when he tells others all about themselves.
Does she really think she doesn’t count? Clearly, there is more to Molly Hooper than meets even his practiced eye.