Inside the mountaintop glaciers of the Pacific Northwest lives a mysterious, and often, overlooked creature. They're small, black, thread-like worms that wiggle through snow and ice. That's right, ice worms! Little is known about them. But one thing scientists are sure of? They can't really handle freezing temperatures. In this episode, NPR science correspondent Nell Greenfieldboyce talks to Emily about how ice worms survive in an extreme environment and why scientists don't understand some of the most basic facts about them.