When a bat makes its noises, the sound waves move away from the bat. If they hit something, they bounce back to the bat (this bounce is called an "echo".) If nothing bounces back, the bat knows there is nothing in front. They use this echolocation to catch their food, like butterflies or dragonflies. When a bat begins its nightly exploration, it usually sends out about 10 calls per second. From the echo they know what is in front. When they get an echo from something good to eat, the calls increase up to 200 calls per second. This increase of sounds is called a "feeding buzz". The bat makes a feeding buzz to sense all the quick moves of the insect it is trying to catch.