The Dzus fastener was loose, but wouldn't come free until the crankshaft was rotated enough to open the valve, allowing the offender to be lifted out with a magnet.
This was a running bike when Mark recently acquired it so he has no idea how long or how many miles the little guy has been rattling around in there. Amazingly, there's no apparent ill effects to the engine nor the fastener.
This is a great reminder for all of us to keep these engine openings plugged at all times — and keep track of our fastener hardware!