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 of 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. ’”

“We 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 protest over her treatment of the mule when she looked at me and quietly said，‘That’s once. ’”