Snakes have a small opening just behind their tongue called the glottis, which opens into the trachea. Unlike what mammals have, the reptile glottis is always closed, unless the snake takes a breath. A small piece of cartilage just inside the glottis vibrates when the snake forcefully expels (pushes out) air from its lungs. This produce’s the snake’s hiss sound. Snakes are able to extend their glottis outside of their mouth while they eat, which allows for respiration while they consume (eat) large prey.
The exchange of oxygen in a snake occurs in the section of the right lung near the head, where its blood vessels are found. The lung portion that is nearest the tail is more of an air sac – no gases are exchanged here, as there are no blood vessels in this part of the lung. In humans both lungs work to exchange gases and both lungs contain blood vessels to exchange oxygen for carbon dioxide.