Chris is on the invisible bench already
Martin: (walks up to Chris)What are you doing?
Chris: Sitting on this here invisible bench.
Martin: Can I join you?
Chris: Sure!
Repeat until all but one of the Campers are sitting on the invisible bench.
Aviva: what are you doing?
Chris: sitting on this invisible bench.
Aviva: How can you? I moved it over there yesterday! (pointing somewhere else.)
All the campers sitting fall down.