The Doctor told him there is a simple informal test the husband could perform to give the Doctor a better idea about her hearing loss.
"Here's what you do" said the Doctor "stand about 40 feet away from her, and in a normal conversational speaking tone see if she hears you. If not, go to 30 feet, then 20 feet, and so on until you get a response".
That evening, the wife is in the kitchen cooking dinner, and he was in the den.
He says to himself "I'm about 40 feet away, let's see what happens".
Then in a normal tone he asks "Honey, what's for dinner?" No response.
So the husband moves closer to the kitchen, about 30 feet from his wife and repeats "Peg, what's for dinner?" Still no response.
Next he moves into the dining room where he is about 20 feet from his wife and asks "Honey, what's for dinner?" Again he gets no response.
So, he walks up to the kitchen door, about 10 feet away. "Honey, what's for dinner?" Again there is no response.
So now he walks right up behind her. "Peg, what's for dinner?"
Spoiler:
