What is Sound?

Sound can't be seen -

It moves like wind over the seas.

Overhearing birds at song,

Mother Nature's word is heard by everyone. 

Underneath the deep blue sea,

Blue whales sing to their babies' glee.

Nothing can't be heard by Mother Nature's song 

As she can be heard by everyone.

Down in the earth below

Sounds can be heard by friend or foe.