mamachari. When he loosened the part that holds the valve in (second from right at top, second from top at lower right), the valve doohickey shot out and hit the roof. He found it, but what if he hadn't? In my own experience I've had the rubber part that goes over the valve doohickey (see fingers) dry out like the eraser on an old pencil. It holds air until you loosen the valve to add more air, because the dry rubber won't block the air when the valve is back in place. So it's always good to have a spare little strip of rubber tube like the one in the upper left corner at the ready whenever you're putting air in a tyre that hasn't been ridden in a long time. (And oh yes, the only thing my daughter swallowed as a baby was that little valve doohickey, which perhaps is the reason I scanned this image back at around that time.)
I suppose it's not even ironic that the type of valve probably most common the world over, from Shanghai commuters to Taliban couriers, isn't even known about by avid cyclists in the United States. I've also seen them on sale in the U.K. The store Bicycle Workshop has a setup on the counter with three valves (dunlop, schrader, and presta) so customers can point to them if they don't know their names. Dunlop valves originated in England so I suppose there's still a lot of them around.