Why are snakes deaf?

Rattlesnakes are deaf and cannot hear their own rattle, a trait that has sparked two main theories on why they have a rattle at all. The first theory, the Bison theory, states that the rattle evolved to reduce the risk of being stepped on and crushed by bison, and secondly, as a means of warning any bison about not to come too close. The other, but less accepted, theory is that the rattle evolved as a specialization of the enlargement of the tail present in most snakes due to the shedding of skin. Later, this evolved into whatever purposes the tail of rattlesnakes has in today's species. The problem with the latter theory is that it does not give a true explanation of the purpose of the rattle, it merely explains how the rattle could have evolved.