Kiai

Rule:
The 'roar' must be totally unintelligible.
(I guess at least in your language, but ideally in ANY language.)

It should be just a wild roar, without indicating / being perceived to be indicating any meaning. The meaning doesn't matter, the *presence* of a meaning is already a breach of the rule.

Bear that in mind; I see Kiai as a way of 'revving up' one's capacity. Not only in a psychological but also in physiological sense.

Imagine a good motor revving. You know a good roaring makes you feel accelerated and gives a lift to your spirit.

Find a Kiai that you feel good, and do it.