"Then it gets really crazy because then you can change how gravity works. You can press a button and you're underwater. Then you press a button and play things in space where there is no gravity," Zuckerberg said animatedly.
Of course, one can't actually play ping pong under the ocean, but that's the magic of virtual reality to Zuckerberg.
"You can experience things that aren't even possible in the world," Zuckerberg said. "That's where I'm really excited."
Zuckerberg is a huge fan of virtual reality, and led Facebook's $2 billion acquisition of virtual reality maker Oculus in 2014.
They're not only planning crazy versions of games, although ping-pong in space does sound cool. Virtual reality also can also allow people to experience things that actually did happen, Zuckerberg explained later in the Q&A.
For example, you can send people videos of a baby taking their first steps, but it would be an entirely different moment if you could experience that in virtual reality and be there when it happens.
"You want to be there, and be able to send it to your grandmother across the country so she can be there, too," Zuckerberg said.