"Those things'll kill you," he grumbled, snatching the cigarette from the teenager's grasp. Just another kid bunking off school, he thought to himself as he stubbed the thing out and met the boy's defiant stare.
"You can talk," the little rascal shot back, clearly unimpressed. "How many so far?"
"What are you on about, kid?"
"Tell me. Is it three or four since this morning?"
He blinked, barely avoided gaping. "How do you – ?"
"Ash on your coat," the boy shrugged. "Plain as day, really."
(Only years later he would realise that was the first time he'd met Sherlock Holmes.)