Actually, the clever and cunning "subject" did not act as planned, Keith only lowered the two cups on top, while the bottom cups he shuffled without raising.

Or so I think.

It was a very entertaining clip, but I expected that little something extra from TED, such as how the mental manipulation is done, to help us learn to... ummm... defend ourselves from predatorial bastards, in a Penn & Teller style lesson.

I was thinking there could be a difference in texture as he touches them..such as an edge that isn't sanded down or something.

Okay, so here are my guesses:

Passenger Seat Catherine was given a different set of goggles. His had LCD monitors fed by the not-so-hidden cameras. And the streets were closed, maybe private land. "I couldn't see through the blindfold. The car was not gimmicked or tricked in any way. The girl I'd never met before."

I think Coke Bottle Nicole was a trained accomplice. Watch how he selects her at 6:00. She's a slightly uncooperative guest, to build credibility. There's no way they'd have embarrassed Mike like that if he were a real guy.

Hand Raising Dude was unwittingly leading, not following. He may also have been a plant, but was wearing white sandals with black socks, so my guess is he wasn't expecting to be on stage.

The coke bottle broke from an exothermic reaction between the shard of "glass" and some chemical inside the bottle. This is too dangerous for an untrained volunteer.

For Steve, the cups, not the plinths are marked. He memorizes which cup goes with the spike at the time he handles them. The blindfold is manipulated at 17:35. He twiddles it with his fingers to open a peephole for his left eye. He sees that cup #1 is the spiked one, so he guides Steve's hands into position over cup #2 (He's got a routine sequenced for each of the four possibilities.) In the 50% possibility that Steve makes the wrong choice at the finale, he's got a contingency he didn't need to use. If he somehow makes a mistake, the spike is not too dangerous.