My passenger was a 17 year old lad from St. Pete to the Florida Panhandle; he had helped me move a boat and I had promised him a flight home. He was, already, a heavy smoker.....
Approaching a military air station, the enroute controller asked if we could please climb to 11,000. I replied no problem. Informed my lad that the military controller had asked us to climb up rather high, and that I would be OK, but that as he was a smoker, he might have a bit of a problem, and to let me know if his fingernails began to turn blue.
He spent the rest of the flight nervously examining his nails......