"Pass me a pen." Sherlock called out into the empty apartment. No one answered. Sherlock kept thinking. But his mind kept straying. Straying to one particular thing, well, person. John. He couldn't think straight about the problem at hand. He couldn't even remember what the problem at hand was. That couldn't be right. His mind was like a computer, an android without feelings or a heart. Computers don't get distracted. If they do, they malfunction.
He kept wandering to minor details, such as John's limp, so slight that it could almost pass as normal. Almost. But Sherlock noticed it. Sherlock noticed everything.
The brown eyes that seemed so focused, so logical. They helped him reason with humanity, however horrifying that thought might prove. He heard Mrs Hudson clattering around her apartment downstairs. That woman made an awful lot of noise, he thought.
When John came back at last, he was sitting on the edge of the couch, hands pressed together, looking straight ahead. In all that time John had been out, Sherlock had done not even a tiny bit of thinking about the case.
Sherlock stretched his hand out to John. "I said can you pass me a pen?" His tone was nonchalant, but demanding.
"When?" asked John, taking off his jacket and tossing it carelessly onto the coat rack.
"About an hour ago." Sherlock replied.
"Didn't notice I'd gone out then," muttered John, tossing him a pen. Sherlock caught it with one hand and went back to his sort-of musings.