They'd have had horses and a cliff back then...

I think the idea is that it was able to sustain its flight via purely human locomotion with the same physics as a bird's wing, i.e. if the human didn't become fatigued it would have been able to fly like that indefinitely (and without a propeller).

There'll be three more if the flapping actually makes it gain height. And come on.. Impossible is nothing?? Towing a glider with a car?? Really?

If you'll look closely, the second or third flap does cause it to gain some altitude; it's just really, really hard for the pilot to generate that kind of force. He had to muscle train for months and drop 20 pounds.