A zen master sits in the hall and hits the ground with a stick. A loud bang echoes across the hall. What heard that?

Through endless kalpas without beginning, whatever you do, wherever you are, that’s your real mind, that’s your real buddha. This mind is the buddha says the same thing. Beyond this mind you’ll never find another buddha.
Bloodstream Sermon, Bodhidharma

It strikes me, that sitting in meditation, being aware of one’s breath is the same. What is aware of the breath?