A couple was watching a Discovery Channel special about an African tribe whose men all had penises 24 inches long. When males reach a certain age, a string is tied around their penises and on the other end is a weight. After a while, the weight stretches the penis to 24 inches.
Later that evening as the husband was getting out of the shower, his wife looked down at him and said, "Whadaya say we try the African string-and-weight procedure?"

The husband agreed and they tied a string and weight to his penis. A few days later, the wife asked the husband, "How is our tribal experiment coming?"

"Well, it looks like we're half way there," he replied.

"You've grown to 12 inches?!"

"No... it's turned black."