What was Simard's first "aha" moment that there might be more to how trees coexist than we know?

Her “aha” moment was when her dog Jigs fell into the outhouse by the lake. She realized that there were roots and other layers that made up the forest.

Explanation:

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.