Birthday shellebrations

Harriet the tortoise with Terri and Steve Irwin. Photograph: Australia Zoo/Reuters
Australia Zoo in Queensland - run by the rambunctious reptile fan Steve "Crocodile Hunter" Irwin - is not for the faint-hearted. There's a 600kg crocodile called Agro, and a 23ft reticulated python called Lily.

But when I visited a couple of years ago, it was Harriet the tortoise who transfixed me, not least because she lays claim to the title of the oldest animal on the planet. The zoo's celebrating her 175th birthday today, despite the fact that it's impossible to know exactly how old she is, let alone on which day of the year we should be breaking out the birthday candles.