THE KIAI.

Every martial art has it's own 'kiai ' or cry so to speak, generally considered to be somewhat terrifing, often thought of as a sharp or instant release of energy, rendering the assailant momenteraly paralised in fear. A romanticise interpretation of the kiai which as made it famous in the west is 'Cry that kills'. The kiai in truth is 'a wave length' set up between two forces. Who ever has he greatest amount of energy or (ki/chi) will show this through the kiai.. As was said an inhibition can occur for a fraction of a second, long enough for the 'kiai master' ,to immobilize of if needs be, completely illiminate his/her assailant, It has also been said that some, 'kiai masters', can attune this action to the point of  paralising smaller animals, of even causing it to drop at their feet. In this instance, the technique would be used to make the 'kiai', the force for a hypnotic energy, to render the animal only fo a brief moment.
The 'kiai' must be produced from the stomache, from the core of true energy; it would be ineffective, and no more than a sound if produced from the throat. The kiai, in actual fact can be thought of as the scinece of using energy.
' Vibration has always existed at both the beginning and the end, with the earth and the universe having lived beten the two.' On this ancient Shinto thought rests an esoteric understanding. The vibration is seen as a sound in the mind (specific state of energy).
To realise the power of sound is to make energy vibrate, and to make life itself vibrate.
Everything can be explained by sound, or rather by the vibraion modes of sound. This knowledge, confirmed by a number of scientific applications (the power of sound over plant/animal life to be more specific) help in understanding why the kiai or so much more than just meer cry and is able to express its energy in all areas of existance. In this instance he kiai could very well be silent, mot af all implying an active decision by the mind, where the strongest will us his influence over the weakest.
The kiai is controlled by the hara or fukushiki kokyu, as known by the Japanese. Some okinawa practitioners would alo achieve this with what is known as 'Sanchin Breathing Kata'.
The kiai is most surely a result of the correct type of breathig, keeping in tune with the mind. The life force control chi making the hara vibrate. The Kiai can be a means of projecting, mental, physical as well as psychological energy. Which in turn explains why  the word KIAI is opposite to AIKI.