A farmer owed a debt to an ugly old man who proposed to annul the debt if he could marry the farmer's daughter. The old man said he would put two pebbles in a bag - if she picked the black pebble she would have to marry him, and if she picked the white pebble she wouldn't. However, the daughter noticed he had put two black pebbles in the bag. Rather than pick, she dropped the pebble on the ground, then said she would remove the other pebble to determine which she had originally picked. Since the second pebble was black, the first must have been white, avoiding the marriage.