Here’s an excellent look into some of the cave systems of the American South East over at NPR right now. One part looks similar to a scene coming up in Underground, so we’ll be studying it closely…

“Each bat was assigned two others it had to distinguish between,” Dr Yovel explained. “So we trained bat A on a platform, playing a sound from bat B on one side and from bat C on the other. He had crawl to where the ‘correct’ sound was coming from.” More at the BBC.