Keeping air in the lungs without releasing it, such as when swimmingunderwater, when trying to be quiet, or when anxiously expecting an outcome. Visible as the mouth being tight-lipped and the cheeks puffed out.
When underwater, a swimmer needs to hold on to as much oxygen as they can, but must resurface after a short time to breathe again. Without resurfacing, an excess of carbon dioxide will poison the blood with carbon. That and a combination of water entering the lungs can lead to drowning.
