"What the hell are you doing?"
"It's an experiment."
John shook his head exasperatedly and proceeded to the kitchen to unpack the groceries.
"You know, not that I expect it, but it'd be nice to come back home sometimes and find something else than you slacking on the sofa, surrounded with endless mess."
Sherlock just hummed in response, never tearing his eyes away from the cage on the coffee table. His palms were pressed together as it was usual when he was thinking, deducing something.
John eventually limped into the living room and claimed his armchair. He gave out a long sigh, the one that indicated a long day, and then turned his attention back to Sherlock.
"So? Mind explaining?"
Sherlock smirked. He liked when John was asking questions.
"Operant Conditioning Chamber. Used in animal behavioral study. Basically, it's a cage with two buttons; one lets the rodent have food, other induces negative experience. Borrowed from the deposit at Bart's, hardly anyone knows this kind of stuff i