The cute and cuddly koala is capable of making as much noise as a one-tonne cow - and it has something to do with the mating call.
Scientists have discovered the anatomy behind the strange bellow that males make during mating season.
Male koalas have very long vocal tracts that are so unusually specialized, that they are able to make sounds that make them sound far larger than they are, BBC reports.
The study, published in the Journal of Experimental Biology, used medical imaging to reveal that a male koala's voice box, or larynx, sits very low in its throat.
This "descended larynx" was thought to be a uniquely human feature - something that allows us to make the sounds we need for speech.
Researcher Dr Bill Ellis and animal vocalization expert Ben Charlton found that a koala weighing just seven kilograms can make a sound equivalent to a cow.
"They are really making themselves sound a lot bigger than they are," said Dr Ellis, ABC reports.
"In humans, when we grow up and become adults, our larynx gets lower and lower. This is thought to be involved in complex language; being able to actually speak and have a more complex language, the deeper your larynx is."
Dr Ellis said that other koalas may be able to discern how big a koala is by its call, and larger males produce more offspring than smaller ones.
"What we think is happening is that the female hears the bellows of the males, they can identify individuals and they can also tell how big they are, and they use this when they go in search of mates."