A forest can feel like a place of great stillness and quiet. But if you dig a little deeper, there’s a hidden world beneath your feet as busy and complicated as a city at rush hour. In this story, a dog introduces us to a strange creature that burrows beneath forests, building an underground network where deals are made and lives are saved (and lost) in a complex web of friendships, rivalries, and business relations. It’s a network that scientists are only just beginning to untangle and map, and it’s not only turning our understanding of forests upside down, it’s leading some researchers to rethink what it means to be intelligent.  Produced by Annie McEwen and Brenna Farrell. Special Thanks to Latif Nasser, Stephanie Tam, Teresa Ryan, Marc Guttman, and Professor Nicholas P. Money at Miami University.  Correction: An earlier version of this story misidentified naturalist David Attenborough as his late brother, actor Richard Attenborough. In addition, it dated the earliest scientific studies of fungi to the late 19th century, whereas naturalists have studied fungi since the 17th century. Lastly, we mistakenly stated that the oxygen that a plant respires comes from CO2, when in reality it comes from water. The audio has been adjusted to correct these facts. Support Radiolab by becoming a member today at Radiolab.org/donate.