Got to be a part of the show at the Rio the night before Thanksgiving 2013!
During the "Bullet Catch" trick where they fire Colt .357 revolvers at each other, I was invited up to the stage by Teller. There is a line on the stage floor separating Penn from Teller and another volunteer was on Penn's side. My part was to inspect the pistol, ammunition and the glass square on a tripod. Teller had me write my initials on the bullet and Penn asked me to draw a picture on the bullet case.
After firing at each other, Penn dropped the fired bullet out of his teeth into my hand and asked me to verify my initials were still on it. (Of course it had my initials on it)
Teller and I were able to have a nice conversation while Penn was speaking during the set up ( he speaks a lot).
I've been a fan of these two since they started in the late 1970s while I was in high school, so it was great to meet them in person, plus I got to keep the bullet and case from the act!