A hihi is a type of yokai resembling a huge monkey with long black hair, a wide mouth and large flapping lips. While it generally eats wild beasts, it is also known to prey on humans, particularly women. When it captures (or even sees) a human, the hihi will run off laughing (hi-h-hi) with its catch. The way to escape is to make it laugh, as when it does, its huge lips with flap up to cover it's eyes, leaving it temporarily blinded. Ideally you should then strike it's forehead with a sharp stake, but failing that, at least it may give you time to hopefully run away.

Utagawa Kuniyoshi
The hihi is also prized for its blood which can be used as a dye, but it is also believed that if you drink it you will develop the ability to see demons and spirits. Some even believe hihi can read the minds of humans. Like many yokai, it is thought that when monkeys reach a very old age, they are able to transform into hihi.
Toriama Sekien
'The Warrior Slaying the Giant White Hihi' - Utagawa Yoshitora, 1859.