I changed the cassette on a wheel today, and when I stuck the QR back in, I accidentally popped an aluminum bushing out of the other side of the axle. The bushing flew, as if by magic, directly into a 1/2" knothole in the pine flooring and vanished. Below the floor is 12" of insulation and then the basement ceiling.
After a few minutes of disbelief and foul language, I remembered that I own a borescope (a flexible fiber-optic scope). I threaded the scope down the hole, through the insulation, and could see the bushing lying on the basement ceiling. I rubber-banded a magnet to a piece of copper wire and stuck it down alongside the scope -- managed to get it right up against the bushing -- won't stick to it. Of course. Because it's aluminum. More cursing.
I took the magnet off the wire and bent a small hook on the end and repeated the procedure. I managed to get the wire through the bushing and ever so slowly pulled it up, and got it out. The whole process was exactly like the old game Operation, except with a lot more bad words.