Yat Lung Wong's training

Hi folks,
I've got a question: Yat Lung Wong (or Wong Yat Lung) gets a hard training by the old Master, and one of the exercises is really exceptional - never seen anything like this - there's a structure made of two wooden poles connected by a horizontal third one; from there hangs down a rope with some thick piece of wood (or leather?) attached to its end (about the size of a big pineapple, I would guess); now Wong takes this into his mouth and clamps his teeth and lips around it.
And then he HANGS FREE IN THE AIR, for about two minutes or even longer!!
How is that possible? I mean, is that feasible at all?
I suppose there must have been an invisible rope (maybe a thin nylon-type wire) somewhere below so Wong could stand on it... or some non-reflecting, transparent plastic plate, thick enough to bear the actor's weight... What puzzles me, is that we can see Wong, at one point of that "training unit", swirling around free in the air, still with that sort of "gag" or "pineapple-shaped thing" in his mouth, and still not dropping to the ground! How did they do that?
I must admit that I liked very much Wong Yat Lung's performance :-)
...indeed a "crafty kid", as one of the reviewers called him appropriately... but IMDB doesn't even list his name in the cast (or did I overlook something?)...

Kind regards
sprendlinger