...Stepped On A Pop-Top...
a-mile-and-a-half into a ten-mile loop (going east on 10th Ave North, just after the intersection with Haverhill Road).
http://i1341.photobucket.com/albums/...AllBolts-1.jpg
I was certain (isn't it obvious?) that it was a humongous sheet-metal screw, but noooooo
http://i1341.photobucket.com/albums/...AllBolts-2.jpg
Walked the both of us back home. Repair? Maņana.
Note: That's a fairly new tire -- Continental "SpeedRide" 700x42 -- with only 1,652 miles on it. Really negligible tread wear, too. Patch the tire? Toss it? (I've got three new ones, but...)