Can You Hear Me ?

John and Mary were getting old and John felt his wife was losing her hearing.
He decided to stage a test. One day, as Mary read the paper, he stood a distance behind her chair and said, in a conversational voice :
- Can you hear me ?
Silence.
He moved towards her.
He was now 6 feet away.
- Can you hear me ?
Still silence.
Finally, he moved directly behind her chair and bent over, just inches from her ear :
- Can you hear me ?
Mary replied :
- For the third time, John, yes I can !