We're used to seeing koalas doing very little - sleeping in trees or just hanging about. It's not often you get to see them doing this.
Scientists have been studying the sound produced by male koalas.
They make a deep grumbling sound when they want to communicate with one another.
The grumbles come from a special sound-producing organ not seen in any other land mammal.
While other mammals, including humans have one set of vocal folds, koalas have two which is why the small creature can make such a deep sound.
Benjamin Charlton, of the University of Sussex, who led the research said: "The first time I heard a koala bellow I was genuinely amazed that an animal this small could produce such a sound."
The pitch of the bellow, Dr Charlton said, was about "20 times lower than would be expected for an animal of its size".
"[It is] more typical of an animal the size of an elephant," he said.