what happens when you breath in and out?
 When you breath, the outside air pushes into your windpipe  into your lungs. When there is a hole in the chest wall, the outside air can come in through that hole. The air gathers around the lung and collapses it. With a large amount of air around the outside of the lung, it can't expand. When you breathe out, or exhale, your diaphragm relaxes and moves upward into the chest cavity. The intercostal muscles between the ribs also relax to reduce the space in the chest cavity. As the space in the chest cavity gets smaller, air rich in carbon dioxide is forced out of your lungs and windpipe, and then out of your nose or mouth. Breathing out requires no effort from your body unless you have a lung disease or are doing physical activity. 