Sometimes bats perceive a smooth, vertical surface as an open pathway, a dangerous error near buildings with glass facades, shown by injured or dead bats next to birds found underneath. The smooth surface reflects the echolocation calls away from the bat until shortly before collision and therefore acts like an acoustic mirror. Researchers of the Max Planck Institute for Ornithology in Seewiesen studied echolocation and flight behaviour of three bat species experimentally and in the wild. They observed them trying to fly through a smooth, vertical plate. However, bats seemingly also manage to avoid these collisions. Here, the number of echolocation calls and the time the animals spent in front of the surface influenced the probability of collision.