How does a Koala eat tough eucalyptus leaves?

Eucalyptus leaves are tough, toxic and low in nutrition, but the koala's digestive system is capable of removing the toxins, filtering them out by the liver. The caecum, which comes off the main intestine, has millions of micro-organisms which break down the fibrous eucalyptus leaves, changing them into digestible nutrients and thus making them easier for the koala to absorb.