A few years ago I was going through airport screening, when they were putting our shoes through a "sniffer" for explosives. Suddenly I was whisked away (and none too gently) while surrounded with drawn weapons.
I was ordered to strip naked, and had just started to undress when a TSA officer came over carrying the grey plastic tub with my pocket items inside.
"It's OK, he was carrying nitro pills," he said, and everyone relaxed. Seems when I had put a new, unopened prescription nitroglycerin bottle in my pocket for my heart that morning, and subsequently put on my shoes, some of the nitro got onto my fingers and then onto my shoes. That in turn caused the detector to alert on my shoes.
A scary moment, but I was also kinda happy that explosives detection devices are that ultra-sensitive. I just hope that terrorists aren't using that trick, and TSA requires some proof of a legitimate prescription for medical nitro, as I had.