Snakes "hear" vibrations.
Credit: Blair Bunting | Dreamstime.com
Snakes have no visible ear, so they don't hear sounds as we do.
But it's not quite right to say that snakes are deaf. They have vestiges of the apparatus for hearing inside their heads, and that setup is attached to their jaw bones, so they feel vibrations very well and may hear low-frequency airborne sounds.
It's though that the hissing sound snakes make is purely to warn other creatures, because presumably snakes can't use sound to communicate with each other.