One day, they were swapping jokes and tales that they heard picked up from varying places and, as such things are wont to develop, they found they were trying to outdo each other in increasingly sillier and/or tasteless jokes. After one such tale (involving a woman who was fair of hair), there came this exchange between the couple.
Naturally, this was slightly worrying to the husband. After all, you would expect him to have noticed some clue or other as to his wife's anatomy during the years of their marriage. In the end, he put it down to the fact that a Gem had manifested. Such things, as everyone well knows, have a life of their own and bend idle chatter to their own ends.
And so life continued, suitably baffled and somewhat entertained.