I've ridden on my Michelin tires for about 400 miles now, and I decided it was time for a tire exam.

I looked at every inch of tire surface and i found a few tiny slits. Two of them had something embedded in them. It was easy to get the first chunk out (GLASS!) but then there was another. I couldn't get it out with my hands so i got a pair of tweezers and pulled it out. it was about the size of this "o" a rather jagged piece of glass.
if i had continued riding on it, i am sure it would have eventually gotten to the tube.
That was an easy maintenance fix1