Sitting on nothing!!!

I've seen this magic trick in real life before. How does it work? I have suspected it had to do with a mannequin. I first noticed it when I was in Vegas. It seemed like a mannequin just perching a hand on a pole. Later, I returned to that spot to find a hole in the ground where the pole was. Yeah the way he behaves is not normal behavior for a man. Anyways, just now I have found out that this magic trick can also involve someone real! For more info on how https://www.youtube.com/watch?v=MmCcR_7WNuU This is mind boggling for real.