Eucalyptus trees coat their leaves with toxic oils to scare off insects and animals. It mostly works - almost nothing eats them. But somewhere along the way, koalas evolved a special enlarged liver organ called the caecum that can detox eucalyptus toxins. So koalas can chow down on what would poison every other mammal.
The price is steep. Eucalyptus leaves are tough, low in calories and full of fibre. Koalas have to sleep 18-22 hours a day just to save enough energy to digest them. A koala on amphetamines would still look kind of sleepy.
That oily eucalyptus also makes Australian bushfires terrifying. The oil vaporises in heat and ignites in mid-air above the canopy. Whole groves can explode into a fireball that leaps a kilometre, leaving trees underneath barely scorched.
