Snakes do not have ears outside the head as we do, nor do they have ear openings or eardrums. We have parts of our hearing apparatus, called the inner ear, inside the head, and snakes have these parts also.
When a person or animal walks, it makes vibrations that pass through the earth to the body of the snake. It has been known for a long time that snakes can feel vibrations from the ground. The vibrations pass through the skin and muscles of the snake to a bone connected to its inner ear. From this bone, the vibrations pass to the inner ear, which "hears" them.
It is now known that snakes can also hear noises or vibrations that travel through the air. The vibrations caused by noises are also called sound waves. When people and most animals hear, sound waves strike the eardrum and go to the inner ear, which is sensitive to the sound waves or vibrations. Snakes do not have eardrums, but their skins, muscles, and bones carry the sound waves to the inner ears. In this way snakes can hear sound carried by the air, but probably not as well as we can.