Fire
Euthyphro>Pre-Socratic>Heraclitus>
Branch Note:
"You can never step in the same river twice"
Important phrase - Always Becoming
He chose fire, because it is always changing - it is never the same.
The objection to this was the simple reality that there are somethings that are static, not dynamic.
His proposition flies in the face of our clear experience of the world. (Same is true of Parmenides, even though their positions are polar opposites)