You've just dropped a tiny, valuable, irreplaceable, critical piece of unobtainium. Searched everywhere and it's nowhere to be found.
Watch your step, could be stepped on. Maybe stuck to your shoe.
Find something of the same size, shape, and weight. Drop it, same way, same place, just like the lost part. Watch carefully as it drops, how it bounces and wanders, where it goes. Look closely in the area where it ends up. Try it again, repeat.
I've had about 95% success within 3 drops...