This is probably an ancient joke, but it is new to me…

A kangaroo bounds round the Australian outback. Every now and then she stops and a little penguin climbs out of the kangaroo’s pouch. It looks awfully sick and promptly vomits.
Thousands of miles away in Antarctica, a little kangaroo sits in the snow shivering, crying and mumbling to itself, “Damned #$%^&* student exchange program!”