A man leaves home to go fight in the Crusades and decides that his wife should wear a chastity belt in his absence. So he locks her up and gives the key to his best friend.

He tells him, "If I'm not back in four years, unlock my wife and set her free to live a normal life."

The husband leaves on horseback and about half an hour later, he sees a cloud of dust behind him. He waits for it to come closer and sees his best friend.

"What's wrong?", he asks.

"You gave me the wrong key."