Koko-uchi (literally: “tiger’s mouth strike”) earns it name because the hand resembles a hungry jaw. All cats suffocate their prey by crushing their breathing passages, resulting in suffocation.
[photo of a koko from the front and side and top]
Koko-uchi is thrown just like a reverse punch, and is used to crush throats using the web between the thumb and index finger. Because of the extreme consequences of this technique, it is reserved for advanced students, and it is forbidden in kumite.
The setup to wristlocks can also be imagined as a koko-uchi to the wrist.
[Koko uchi fast and slow, from the front ans side several times.]