I saw this wierd play at a theatre in london once...i don't remember if it was the national theatre or not, but essentially it was a double-sided theatre with shared sets. The play was shown on both sides, to two different audiences, at the same time--each audience only saw half the play. So there might be a scene with two chars, who say they are going to go do something, who then walk 'backstage'...except they are headed straight onto the other stage where they do exactly what they said they would do. Then after they would come back or we would see the consequences. It was a bit...odd, but kinda neat.