And it’s even worse. They only eat some kinds of Eucalyptus. They found this out with a koala in a zoo. They supplied him with fresh branches, but refused to eat them. All while trying to get to some eucalyptus tree right next to his cage. They gave him a branch from that tree, which he devoured.

Turned out that the tree next to the cage and the one where they got the food from were different genetic variants of eucalyptus trees that are indistinguishable for normal humans.