SAN FRANCISCO—Google blew away everybody with perhaps the most audacious tech demo ever on day one of Google I/O. On Thursday, Google co-founder Sergey Brin emceed a live recreation of the Project Glass showcase, complete with skydivers leaping out of an airship, BMX bikers racing across rooftops, and a mysterious, plot-advancing package that was again delivered to the third floor of Moscone West.

Why do it a second time? Probably because Google is the kind of company that likes to let us behind the curtain to see how the magic really works (to a certain point—you'd have an easier time persuading Coke to divulge its secret formula than getting Google to spill on its search algorithm). And maybe also to head off any skeptics who suspected the search giant faked all or parts of Wednesday's high-flying stunt.

So on day two of Google I/O, Brin again took over the morning keynote, this time via video feed from atop the 110-foot Moscone West building where the event was being held. He took viewers through the stunt step-by-step, which you can see play out in the slide show accompanying this article and in the video below.

How did the production team manage to maintain a signal from the rooftop to the airship circling above downtown San Francisco? Calling it a "very challenging" wireless environment, Brin pointed to team members holding handheld transmitters to beam a signal to the Zeppelin, where the skydivers were hooked up via their Project Glass goggles. Brin, meanwhile, had ditched his clear Google Glass spectacles for a pair of augmented reality shades that looked a lot less geeky, if you ask me.

So for a second time, we were treated to a mix of HD video and a Google+ Hangout stream powered by Google goggles that showcased one truly gutsy tech demo.

"A million things could go wrong," Brin said again just as the airship doors opened and the skydivers above prepared to jump into thin air. But once again, everything went off nearly no hitches—Brin looked like he banged into some metalwork in his haste to hustle across the rooftop, but happily he was the only one who got hurt.