Have you ever felt the tickle? A little nudge in the back of your throat that indicates an issue with the oxygen supply? It can start small, a truly minor sensation. But as time passes, that insignificant sign will escalate to a cough or a wheeze or a sudden inability to breathe. Somehow, in some way, you’ll be made to understand. I only hope that you’ll get the message before you end up as the coal-miner’s canary, your body stiffening on the floor, trampled by people running for the lives they still possess.