Now, as our diaphragm flattens down and as the ribcage increases, that increases the volume inside the intraplural space, and that decreases the pressure inside that space. And eventually, the pressure inside the space will basically decrease to a point where it will be lower than the pressure inside our lungs than atmospheric pressure. And at this point, there exists a pressure gradient, a difference in pressure, such that inside the intraplural space, we have a low pressure and in the outside of our body and inside the lungs, we have a higher pressure. And at that particular point, when the intralural space has a pressure that is lower than the pressure inside the intrapulmonary area, then our air will begin to move down its gradient, down the pressure gradient from a high pressure to a low pressure. So, in the same exact way that a marker or any other mass will always move down its potential gradient, gravitational potential gradient, from a high potential to a low potential, molecules, air molecules will also always move from a higher pressure to a low pressure. And that's exactly why when the diaphragm flattens down and when the external intercoastal muscles contract and expand the ribcage, that increases the volume and decreases the pressure inside the intraplural space.