We once got a flat in a rental car on Maui while driving around near Makena on the south side of the island. But a few days before that, we were at Volcanoes Natn'l Park on the Big Island, and ignoring tales of bad juju for removing lava rock from the islands, I picked up a small piece to bring home as a souvenir of the trip.
Now about the flat. We're driving along in a fairly remote area when the LR tire suddenly goes down. I don't hear a 'pop' or anything, the tire just goes flat, so I put on the spare and stop at the first gas station I see to get it fixed. The guy comes back with the tire and says that he didn't find a puncture or any other damage but shows me what he DID find. In his hand were a few very small lava pebbles that were jammed INSIDE the cap on the valve stem. They had somehow managed to press on the pin and cause the tire to go flat! And the weird thing is that we'd been driving around in that car for a few days before this without incident. Cue up the
'Twilight Zone' theme music.
Needless to say, I returned that pilfered lava rock back to the island ASAP