Now, notice we have a high pressure on the inside and low pressure on the outside because our outside, we're assuming, is a vacuum. Now, we make a very tiny incision, a very tiny hole. And the diameter of this hole is much smaller than the distance between a two molecules. That's our assumption. So eventually, some of these molecules will hit the walls of the container. At any given time, some of these molecules will hit the wall at exactly the spot where this hole is, and they will exit or escape the cube.