"But isn't it unusual to find them so thick?" Bob asked.
"Indeed it is. I happen to know that as a usual thing not more than one oyster in a thousand has a pearl in it and probably not that."
"Then what makes them so thick in these fellows?" Bob asked.
"I'm not sure, of course, but, you know, it is thought that a pearl comes from a grain of sand getting into the oyster's shell and setting up an irritation. Now, you may not have noticed it, but these oysters are slightly different from those we're used to not only in size but in shape as well. Their shells are more nearly round and are slightly rougher. My theory is that this kind of oyster, for some reason which I can't explain, is more liable to the pearl disease than any other varieties."
"It's a good theory, I'll say," Bob agreed.
"And let's hope they don't get over it in a hurry," Jack added.
"Get over what?" Bob asked.
"Why, that irritation that makes pearls," Jack laughed.