Ever bumped into a glass door? It seems like bats do it pretty often, and not because they’re texting. A new study shows that bats fail to recognize human-made vertical, smooth surfaces, like glass windows, as obstacles. The researchers placed a vertical metal plate in the corner of a flight tunnel. Then, they monitored bats as they flew through it. Of 21 bats, 19 crashed at least once into the plate, but never into walls or other objects Collisions also occurred when the researchers placed the metal plates outside of caves of three different bat species. This is because smooth surfaces limit bats’ ability to navigate through the dark using their echolocation system. Bats emit high-frequency sounds and use the returning echoes to spot obstacles in their surroundings. But a sleek, vertical surface approached at an angle reflects away the echoes, fooling bats into recognizing them as open flyways. The scientists now hope to determine if windows or glass buildings pose an ecological threat to bats and how these animals can learn to deal with them.