Elephant In The Room
A simple particle simulator with a pre-placed escape hole. Or, if you're one of the particles, a terrifying scenario where you desperately want to stay as far away as possible from all others but somewhere in the inescapable room is a being who can't be sensed in any way but whose existence is so in-graspable that mere contact will destroy you....the elephant.
Left click to place a person.
Right click to place a dog.
Middle click to place a car.
Avoid the elephant at all costs.