Secret to a long Marriage

A couple was celebrating their golden wedding anniversary.  Their domestic
tranquility had long been the talk of the town. A local newspaper reporter
was inquiring as to the secret of their long and happy marriage.
"Well, it dates back to our honeymoon," explained the man. "We visited the
Grand Canyon and took a trip down to the bottom on the canyon by pack mule.
We hadn't gone too far when my wife's mule stumbled. My wife quietly said,
'That's once.'
We proceeded a little further and the mule stumbled again. Once more my wife
quietly said, 'That's twice.' Hadn't gone a half- mile when the mule
stumbled the third time.  My wife quietly removed a revolver from her pocket
and shot the mule dead. I started to yell at her for her treatment of the
mule when she looked at me and quietly said 'That's once."