A couple was watching a Discovery Channel special about a West African "bush tribe" whose men all had penises 24 inches long.
When the black male reaches a certain age, a string is tied around his member and on the other end is a weight. After a while, the weight stretches the member to 24 inches.
Later that evening as the husband was getting out of the shower, his wife looked at him and said,
"How about we try the African string and weight procedure?"
The husband agreed and they tied a string and a weight to his penis.
A few days later, the wife asked the husband, "How is our little "Tribal Experiment" coming along?"
"Well, it looks like we're about half way there" he replied.
She said excitedly "Wow, you mean it's grown to 12 inches?"
"No" he said, "It's turned black"