When crushed, the leaves and flowers will have a pleasant, spicy smell. Most folks agree that it smells like rosemary, oregano and other cooking herbs blended together. The leaves should also be hairy or fuzzy, especially on the stems. If the leaves have smooth stems, do not even touch them. If you've already crushed them to smell the plant's odor, go wash your hands immediately. Fool's parsley and poison hemlock leaves look similar to yarrow leaves when they're young, but are very poisonous and fatal if eaten, and will have a bad odor reminiscent of chemicals or cleaners.