Snakes breathe by moving the muscles that surround the ribcage. They lack the diaphragm that drives the respiratory process of mammals. A muscular contraction pushes air out of the lungs. When the muscles relax, the lungs fill with air.
The work of exchanging carbon dioxide for oxygen in the snake's respiratory process depends on the right lung. It is longer than the left and located closer to the mouth. In some species of snakes, the left lung is only slightly developed and serves no essential function. However, the left lung of water snakes helps to regulate the pressure within their bodies as they swim. Between breaths, a snake may pause for as long as a few minutes.