Sherlock thrived on observation. Everyone who knew him was aware of it. He could watch a suspect and know exactly what he'd done (or not done, as the case may be). He could study a stranger and know her entire history. What most people didn't know, however, was that one of his favourite things to observe was incredibly mundane, thoroughly predictable. He'd learned everything he could from this particular routine, and yet he found himself watching intently every time he got to experience it.
John stumbled into the flat, soaking wet. It was wretched outside. He shook himself off. Sherlock was reminded for a moment of an adorably shaggy dog. He smiled to himself and then shook his head. It wouldn't do to think in silly metaphors. John shuffled into the kitchen and Sherlock was on the alert. It was starting.
John made tea as if it were a ritual. Always following the same pattern – mug on the counter, water to boil, steep for three minutes, a dash of milk and sugar. However, it was the final step in his routine that Sherlock loved to observe. John would sit down and wrap his hands around the mug and take in one slow, thoughtful sip. The look on his face, no matter what his mood had been before, was always absolutely blissful.