It had to happen sometime. I had my first flat since I started riding last August. Luckily it was in the garage when i discovered it. I was showing my frankenbike the "Red Ryder to my brother from Las Vegas when he said, "You have a flat!"
Took off the rear wheel, pulled the tube, which still had some pressure, added some air, no leak!
Took the tube inside, put it under water, no leak! Started squeezing the tube in sections under water, finally found bubbles. Obviously, it was a very small hole.
I went back to the tire to look again now that I knew where the leak was and found a tiny black dot showing on inside of the tire, nothing visible on the outside. A closer inspection showed a tiny slit in the tread. I finally managed to extract what looks like a tiny piece of flint. I never would have found it on the road and probably would have ended up with two flats!
I wonder if I should get puncture resistant tires.