Koala bellows with extra vocal folds
2 December 2013 Last updated at 17:42 GMT
It is a low, rumbling bellow that seems very incongruous coming from the mouth of a diminutive koala.
And now scientists have found that these famously sleepy marsupials have a evolved a vocal organ that allows them to produce very low-pitched sound.
Koalas, researchers discovered, have an "extra pair of vocal folds" which they use to make their mating calls.
The findings are published in the journal Current Biology.
In this clip, we see a male koala in a sanctuary in Queensland making the very low-pitched, grumbling bellow.
Footage by Benjamin D Charlton at Lone Pine Koala Sanctuary, Brisbane