At an auction today, to the north of here, I was just starting to examine a trio of large crocks when a fellow walked up and said, "Are they all right?"
I said that I thought so, and of course right at that moment detected a hairline crack in the one I was then examining.
"Know how to tell if they're good?" said this expert. "You rap them with your knuckles. They sound different if they're cracked." He rapped on the crock in front of him. It gave off a low, hollow tone. "This one's good. Rap on that one."
I gamely rapped on the one in which I had found the hairline. It had a higher, hollow tone.
"See?" he said, and walked off.
The crock in front of me was smaller, however: so of course it had a higher, hollow tone. The third crock had yet a different hollow tone -- being yet a different hollow shape.
I resumed my examination, using my inexpert means, and found hairlines in all three.
I left before the auction proceedings reached that building, so can only wonder whether the expert bought the "good" one.
I thought they all sounded good: the three crocks, and the expert. All four were cracked, though.