I was attacking my Aikido partner with a strike similar to stabbing someone with a knife. He was a 6th dan (my sensei's sensei), and was practising the technique first. So we began, and my right hand came down at his head.

He deflected the strike perfectly, sending my right hand harmlessly to the side. Then he did something I didn't expect. I suddenly noticed that his other hand was coming up to my face...

Complete and utter darkness. Nothing. Except for a single horizontal, multicoloured line in the black, like a line of technicolour static. Just the thickness of a hair wide, and stretching completely across my vision.

...a split second later I was lying on the mats, with my partner grinning over me. And I started grinning too.