How to Tell the Difference Between Poison Hemlock and a Harmless Flower, as the Invasive Species Spreads

Let's say you're out for a late summer stroll, and you come across a patch of familiar-looking flowers with long, thin stems and tiny white flowers that grow together in round bunches. They appear to be Queen Anne's lace--a flowering plant you've seen in floral arrangements and may have made crowns out of as a child.