The bats roar at each other like death metal.

Scientists have found that water bats, and probably other types of bats, use throat structures similar to those used by death metallers and Tuvan throat singers to produce a lower growl. These structures are called ventricular folds or false vocal cords, and bats seem to use them to produce sounds at frequencies between 1 and 5 kHz. So animals challenge relatives or warn of danger.