This is an illusion where 13 randomly selected audience members are vanished from a platform on the stage, never to be seen again.It goes something like this...
15 silver beach balls are thrown out into the audience and the audience is instructed to hit the beach balls around as music is playing in the background. When the music stops, the 15 people who are holding the beach balls are invited up on stage.
2 of the people are asked to be witnesses and are instructed to stand on either side of this raised platform. On the raised platform are 13 chairs.
The 13 remaining people are invited up onto the platform (located in the centre of the stage) and each takes a seat in a chair. They are each given a flashlight and are told to wave them around as a curtain is lowered around the raised platform. You can still tell the 13 people are there as you can see their flashlight beams shining through the curtain. In addition, you can see below the platform as it is raised off of the stage by about 3 feet.
About 20 seconds later, the curtain is dropped to reveal nothing but 13 empty chairs - the audience members have vanished and the crowd is in awe. The second before the curtain drops, you can still see the flashlight beams shining through the curtain but as soon as the curtain drops, the flashlight beams are gone.
I was lucky enough to have caught one of the beachballs when I was in Las Vegas in February and I got to be one of the witnesses. As a witness, I was able to see behind and under the platform at all times. This illusion (in addition to Test Conditions) blew me away!
MagicIntern
"Thirteen" 
