I did not know it at the time, but I had a shotgun shell in a small pocket of my backpack. I got through security at both airports on a round-trip before finding it a week after the trip. I can only imagine what would've happened had it been found. I barely made it to the airport for the flight out, and would've been up a creek for missing a meeting if I had missed that flight. I got lucky as heck.
(Thanks again to my guardian angel. He/she must get overtime pay, LOL.)