Answer:
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boon One empty, and one full.
I turn around once. What is out will not get in. I turn around again. What is in will not get out.
What can you catch but not throw?
What is it that no man ever yet did see, which never was, but always is to be?
A morbidly-named body of water
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.