Scientists have figured out how koalas are able to produce a mating call that is so low-pitched it ought to come from a creature the size of an elephant.

The vocalizations are made with a previously unknown vocal organ that researchers have dubbed “velar vocal folds,” according to a study published Monday by the journal Current Biology. When stretched out, this pair of membranes can become more more than five times as long as the koala’s vocal cords. That length allows the animals to produce the low-frequency sound overheard during the breeding season. (You can listen to the decidedly un-cuddly sound here.)

An international team of researchers discovered the membranes by dissecting the larynges of 10 male koalas. At first, all they found were the usual vocal cords, whose average length was 9.8 millimeters. That size should allow the koalas to produce a sound no lower than 51.0 hertz (a frequency that’s between the lowest G and G-sharp on a piano keyboard).

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