Mark Evans and Joy Reidenberg head to Australia to dissect its most iconic animal, and find the marsupials' reproductive organs to be most surprising - the male genitalia is back to front, while the female has three vaginas. Simon Watt heads into the Blue Mountains with Charles Darwin's great-great-grandson in search of other creatures, including a bird that decorates its nest with an assortment of blue ornaments and a primitive mammal that lays eggs like a reptile.