Horse is controlled by the mouth. Therefore you have seen the harnesses are fixed in the mouth, the driver controls the mouth and the horse goes. So Krishna was a boy. How did He know that "This demon Kesi has come in the shape of a horse. If I have to control him, I will have to control his mouth". So He pushed His hand within the mouth of the horse, and the horse felt it was just like a hot iron bar, so he died. Similarly, when Krishna fought with Aristasura, He knew that to control the bull you have to control the horns, so He took up the horns and killed him. This is svabhaviki, natural. He knows everything.
Mayapura, June 17, 1973