Kappa (mythical creature)

A kappa is a mythical creature. They can be vicious and enjoy the taste of blood. A human may escape them by exploting its one weakness - its viltalilty is drawn from a saucer-like deppresion in its head, which must remain filled with water. If one offers a polite and ceremonious bow, the kappa will be obligated to return it. The water will spill and the kappa will be defeated.