Moments when his face shows sentiment. Only when he’s alone or taken aback. Inspired by ”Sentiment is a chemical defect found in the losing side” and “I imagine John Watson thinks love’s a mystery to me, but the chemistry is incredibly simple and very destructive” and of course Benedict’s acting.
After his collision with sentiment in A scandal, Benedict Cumberbatch portrays a more self contained Sherlock in the beginning of the episode. Sure, feelings are there, but he manipulates them more, uses them to get what he wants – see the I need some scene.
But the case brings his mind and body so close to losing the battle against sentiment that he really comes to hate the irrationality of feelings. He ends up hurting his friend and even using him in a brutal way, everything to prove to himself that sentiment can’t stop him from getting to crack the case. But in the end, we see remorse and I think that was the moment, in the final few scenes of the episode, when Sherlock knew John can take it, can take everything, because he knows him and accepts him and his need to be right, at any expense.