"I am medicine that is completely free. I is contagious in the best way. I can defuse a crisis in an instant. I is uniquely human in its complexity. What am I?"

Answer: Laughter. Laughter triggers the release of endorphins and reduces cortisol. It is contagious and socially bonding. Anthropologists note that while other animals produce play sounds, only humans laugh at abstract ideas, jokes, and wordplay.