Disclaimer: I don't even own the format this is written in, but gratefully borrow everything in the hope of bringing a smile :)
With a sigh John tried desperately to concentrate on the words on the page in front of him. Sarah had recommended reading this particular article in the BMJ.
Unfortunately Sherlock didn't share his enthusiasm for the advances in medical science (unless it was he who made those advances) and so he continued to talk.
"Well, I'll just have to conduct this experiment on my own." Sherlock's eyebrows rose as he waited for a response.
"Hmm."
"We need to know how Carter managed to poison her and make it look like natural causes."
"Hmm."
"Well…" The younger man was lost for words, he was so used to John's undivided attention. He flung himself onto the couch to think.
John enjoyed the peace and quiet until, just as he was getting to the crux of the research, his flatmate leapt up and flung a question at him. Glancing up, it seemed he was waiting for a response.
"Um…yeah." It seemed to be the right thing to say, as Sherlock grinned and rushed off up the stairs.
In the silence, realisation hit the doctor.
"Wait! What have I just agreed to….?"
Scrambling out of his chair he chased after Sherlock, finding him in the upstairs bedroom, trying to push a needle through John's mattress.
"Oi! What the hell are you doing to my bed?"