(This is up later than usual– I’ve been without a browser for a few days.)
A woman in China went to visit her married daughter who (according to custom) lived with her new mother-in-law.
The three women had just sat down to the evening meal when a gust of wind blew out the lamp.
“I will fetch a light,” the daughter’s mother-in-law said in the darkness, but the daughter was already rising and leaving the room, so instead the mother-in-law remained.
Thinking she was alone with her daughter, the visiting mother began a lecture on the duties of a host to see to the greatest comfort of her guests, recommending her daughter turn the choicest sides of the serving platter to her mother, in order that she might take the best without appearing greedy.
“Indeed, as the guest is your own mother, nothing less than filial duty demands you giver her the best that may be offered.”
Just then, the daughter returned with light, and the mother realized in horror that her daughter’s mother-in-law was the one listening to everything she said.
“Forgive me,” the mother said. “I have a curious malady with no known cure. It causes me so speak nonsense in sudden darkness, until the light returns and brings me back to my senses.”
The mother-in-law nodded knowingly.
“Ah, yes,” she said. “I understand perfectly, for I have a similar malady that affects me in the darkness. When the light suddenly goes out, I am rendered deaf, and can hear no word until a new light is brought.”
Also from Ragan’s book.