We should have taken more notice of the thump and the shriek. We heard it as we walked past the chimpanzee enclosure just through the gates of Sydney's Taronga Zoo, but we were too busy studying the map and making a plan.
With 340 species over 21 hectares, you need a plan. We discovered this to our detriment on an earlier visit to Sydney when we'd rushed through the zoo between the baby's naps.
We managed to get back to the car before the baby exploded, only for the toddler to ask,
with a rising note of anxiety, when he'd get to see the koalas. Disaster. He had to be content with peering into the eucalyptus tree over the fence and making out a few (possibly imaginary) fuzzy grey bottoms wedged in the branches.
On this present-day assault on the zoo, the toddler was a schoolboy and the baby a preschooler - and koalas were passe.
The kids were determined to track down the meanest, scariest killers. And that's the charm of an Australian zoo - there are plenty. Not just your regular lions and tigers, but killer snakes, killer crocodiles, killer African wild dogs, killer alligators, killer bears, killer spiders, killer snow leopards, even toxic frogs and venomous platypuses.
If it couldn't kill you, or at least cause gruesome injuries, the kids would give the creature a dismissive look and skip past.
We decided, given the ongoing fascination with things with sharp teeth, fangs and poison glands, that while we were in Sydney we would treat the kids to a safari - get out and see a bunch of animals we don't get to gawk at in Auckland.
As well as Taronga, the city has a zoo specialising in Australian animals, two aquariums, two wildlife parks and a museum with two dinosaur exhibits, as well as a squawking, creeping, crawling gallery of wild urban Australian birds and wildlife. (One morning a mysterious crab-like spider the size of my hand appeared in a web in the in-laws' backyard, prompting a rash of unenlightening Googling. Even more unsettling, the next day it was gone.)
At Taronga, the kids weighed up each animal on its capacity for harm.
"Can that kill you?" they asked of the komodo dragon. And the gorillas. And the Tasmanian devil. And every snake and spider. And the red kangaroos. (Don't laugh, they can.)
If the answer was "yes", the kids demanded to know precisely how, in detail. (We did point out that the biggest threats to many of the animals were humans, which they solemnly contemplated for all of a second.)
The kids did make an exception to their morbid criteria long enough for us to go to the zoo's superb Seal Show, where seals and sea lions dived, splashed, barked, and leaped in a pool before us. Despite the lack of blood and gore, they were transfixed. We had to concede that Michi the giant Californian sea lion, who weighs a couple of hundred kilos, could probably kill you if he got really angry. Or if he sat on you.
As the song goes, we stayed all day at the zoo. We were there for an almighty seven hours, and even then we had to make some tough decisions on which animals to skip - sorry, herbivores.
In the end, the biggest scare of the day came from one of the most benign-looking animals. On our way to the exit, we stopped by the chimpanzee enclosure.
The six-year-old attached himself to the glass like a limpet, his nose pressed, watching a chimp scamper past - when the creature swivelled, charged and, with a shriek, body-slammed the glass where Oscar stood. It was half an hour before the boy stopped shaking. Then he decided it was the coolest thing ever.
With one thump, the lions, tigers and crocodiles were forgotten. The scariest animal at the zoo turned out to be the one that shared the most DNA with us. Who knew?
ON THE TRAIL
Taronga Zoo, Mosman: Hugging a hillside overlooking the harbour, Taronga promises a big day out. Take a ferry there from the city, and soar over the animals in the cable car, included in the admission price. The Bird Show and the Seal Show are worth planning your day around.
Symbio Wildlife Park, Helensburgh: Promising a peaceful day out in the countryside, Symbio is a smaller zoo about an hour's drive southwest of the CBD. Offers hands-on experiences, such as feeding kangaroos and emus, and handling snakes. Has native and exotic animals, including tigers, dingos and monkeys, and a swimming pool for the little humans.
Featherdale Wildlife Park, Doonside: Another quieter zoo about 40 minutes west of the CBD, Featherdale is home to Australian and exotic species, including crocodiles, and offers hands-on experiences, including kangaroo, wallaby and emu feeding, and snake handling.
Wild Life Sydney Zoo, Darling Harbour: A deceptively big zoo in a compact space, Wild Life is a great place to see native Australian animals without leaving the CBD. Highlights are koalas, snakes, spiders, butterflies - and Rex, a five-metre salty croc who was taken into custody after he developed a taste for unsuspecting pet dogs.
Sea Life Sydney Aquarium, Darling Harbour: The Sydney aquarium is Kelly Tarlton's on a grander scale. Animals include dugongs, platypuses, rays (including a particularly fetching leopard-print whipray), penguins and three-metre grey nurse and lemon sharks. They're introducing shark-snorkelling, if you're really keen.
Manly Sea Life Sanctuary, Manly: A smaller aquarium that offers a pleasant respite from the sun and sand of Manly beach. Drawcards are grey nurse sharks and a colony of charming little blue penguins.
Australian Museum, CBD: Two dinosaur exhibitions will satisfy the dinophiles in the family. Temporary exhibit Tyrannosaurs: Meet the Family uses techno gimmicks to bring the extinct predators to life, while the permanent dinosaur exhibit features soaring skeletons and life-sized models.