We take an oxygen into the capillaries of our body and we expel our carbon dioxide from the capillaries and to our lungs, eventually expelling them to the outside. Now, once we exchange the oxygen for carbon dioxide, how exactly does exhalation actually take place? Well, once we're at this stage, what happens is the diaphragm and these intercoastal, external intercostal muscles begin to relax. And as they begin to relax, we're essentially moving in the opposite direction along the following curve. So the diaphragm begins to recreate the following dome shape and that pushes on our cavity and it pushes on the space inside. And the Rift cage, as it basically decreases in size, it also forces our volume inside the intraplural space to decrease.