I just remembered this one.
An emperor has a daughter who's of age to be married and he have three suitors who's worthy of her. They're all expert swordsmen, good looking and well educated so he decided to put them to a test.
He summoned the samurais to his throne and told them he must be impressed with their swordsmanship and the best shall win his daughter. For each he'll release a fly from a box and they must kill the fly with his sword.
The first one steps up and the emperor released a fly. Swish! Swoosh! the fly dropped dead neatly cut in halves.
The second one steps up so the emperor releases another fly. Swish! Swoosh the fly fell to the ground minus his wings.
The emperor thinks they're really good and this is going to be hard but let's see what the third one will do.
The third one steps up and the emperor releases the fly. Swish! Swoosh! the fly flew away.
Th emperor said alas! The fly escapes.
The third samurai said, yes your highness he flies away but he will no longer reproduce.