Danish researchers have discovered that bats use low-pitched calls akin to the growls used by death metal vocalists to communicate with other bats during social calls.

In the first study to directly observe self-sustained vibration in bat vocal structures, the University of Southern Denmark researchers extracted the larynx from five adult Daubenton’s bats, a species of bat found in Europe and Asia, and filmed them at 250,000 frames per second.

The researchers found that besides being able to produce high-frequency echolocation calls, the thick folds of membrane just above the bats’ vocal cords, called “ventricular folds,” vibrated at frequencies between 1 and 3 kilohertz. Those folds are likely involved in producing the bats’ social calls.

The researchers said the bats’ use of ventricular folds is similar to how some humans, like death metal vocalists and Tuvan throat singers, use the folds to produce low-frequency vocalizations. They said natural selection may have created distinct evolutionary pressures that expanded the vocal range of bats.

The study can be found in the journal PLOS Biology.