Remember that odd-looking Google Glasses prototype the search giant has been pushing since April — and that co-founder Sergey Brin has been wearing to practically every event since? Well, now we know a little bit more about how they work, courtesy of an unusual source: California Lieutenant Governor and former San Francisco mayor Gavin Newsom.

The one big mystery about Project Glass, the internal Google name for the glasses, is how you navigate through the items you see on their tiny screen. Was the glasses technology sophisticated enough, we wondered, that it could track your eye movements and sense where you were looking? Or did it simply use a trackpad on the side of the glasses, as several sources have suggested?

Now we know the answer for sure, thanks to Brin and Newsom: it's just a trackpad.

Newsom had Brin as a guest on his Current TV show. The episode will air this Friday, but Current has released a short extract, which you can see in the video above.

Brin takes a picture of Newsom with the glasses, and then swipes through what appears to be a picture gallery using the large black area on the right of the glasses. When he hands them over to Newsom — who just became the first known non-Googler in the world to take a look at Project Glass — Brin tells him "don't touch the pad on the side."

Watch closely and you'll see the trackpad appears to swipe in two directions — side to side to view the picture gallery, and up or down to exit and enter the gallery.

Newsom was apparently impressed with the result. "The image was remarkably clear," he told Wired. “You can easily forget you have them on, and sense the capacity of use in the future." (He would not say, however, whether he would wear the glasses himself.)

One mystery remains: how do the Google Glasses take snapshots in the first place? What is operating the shutter? Is that, perhaps, controlled by eye movements? Newsom asked, but unfortunately Brin didn't respond.

Does this video convince you one way or another about Project Glass? Are you more or less likely to wear this thing? Let us know in the comments.