As for your belief in this martial arts stuff -- even if it were true, it would be utterly useless against a gun-wielding character a la Indiana Jones when he was confronted by that clown doing his machete-twirling drum majorette-like showing off for the "true believers" in the audience.
There is actually a purpose to that sword-twirling stuff, but it's not in a fight. I do it regularly to increase the strength and flexibility of my wrists.
Anyway. As has been explained many times, n!nja, there
are rational explanations for the dodging-the-sword trick. Sure, it
seems supernatural, but really what is happening is that you are training your senses to the point where you can detect sounds, air currents and so forth that are actually below the threshold of consciousness. As others have said
several times, you're noticing the shifting of the tatami, the sound of the sensei's clothes, the movement of the air. You may not even be aware that you are sensing them, but that's what's happening.
I would be willing to try to "fool" this sense. I would stand behind you with my sword raised, ready for a strike. You would put on a steel helmet, becaise I'd be hitting you quite hard with a blunt steel sword, and sit directly under my sword with your eyes closed. I would wait motionless for a random length of time before striking. I think that you wouldn't notice the attack, because prior to me actually striking you I make no movement, I do not shift my weight, I do not move my sword out of its position. I would simply strike you in one single sudden move. So long as I am able to remain motionless before the moment of striking, you would have no clues to pick up on to warn you of. It would be as much a test of
my ability to remain motionless in an attacking posture as it would of your ability to detect my movement.
Unfortunately I probably live 10,000 miles away from you, so we're unlikely to be able to actually perform this test.