I used to study Aikido. One day, in the changing room, the conversation came round to Japanese masters who could knock you over without touching you. At this point, the head instructor came into the room. He listened for a while, then asked the person who'd brought the topic up (and was advocating it as true) if he'd like a demonstration.
So, we filed into the dojo, and knelt at the edge of the mat for the domenstration of mystical power. At this stage I was feeling slightly disappointed, as I'd come to this particular class due to the lack of any mysticism, but still interested in what was going to happen.
So, the instructor stood about 10 metres from the student, and started to breathe deeply. He asked the student to close his eyes, so he wouldn't see when the ki strike came in, and be psychologically affected by it. The student complied.
After about five seconds of this deep breathing, the senior instructor shouted and made a sharp gesture towards the student. At this point, a second instructor stood up, walked over to the student, pushed him over then quickly sat down.
The student got up amazed, convinced of the power of ki energy, and totally confused as to why everyone else was doubled up with laughter.