I liked the example of water spilling onto the floor. I was trying to explain this point to my 7-year old the other day. As crazy as it sounds, the laws of physics don't say that the water couldn't jump off the floor and back into the bottle. The laws of physics are equations and equations are equally true if you reverse the left and right sides. In terms of the equations, that water in the bottle equals the water on the floor (along with the increase in heat energy and other effects), so there's no fundamental physical reason you can't go from one to the other. The reason why you don't ever see it is because it is astronomically less probable to happen in reverse.
