The other day, I lost an SPD cleat. I'd not bothered stopping to sort it out, although it was obviously loose and getting more awkward to de-clip. And then, it was gone. Changed shoe the next day and found it very difficult to clip in. Odd. Oh well. Put a new cleat on the old shoe and it wasn't much better. Rode it a few days. Gave the bike into LBS (who had built it) to sort out the brake issue (turned out to be contaminated pads #2. Apparently).
As I collected it, the mechanic handed me a bit of metal with two screws in "You lost a cleat? it was in the pedal"