They might never have killed their own meal. They might have been born in captivity. They might spend their days lazing in the sunshine, being hand fed, dully eyeing kids pressed up to the glass. But don't let that fool you.
They're the most dangerous predators in New Zealand and, given a chance, they'll shrug off a lifetime of conditioning in a micro-second for their one chance at a kill.
And that's why we love 'em. Admit it: you don't go to Auckland Zoo or Butterfly Creek or Kelly Tarlton's to gape at the eastern blue-tongued skink or the clown triggerfish, as fascinating as their life cycles might be.
You go to see the animals that plant a bit of fear in you and that might at any moment test the security of that fence or safety glass separating you.
In New Zealand it doesn't get more scary than big cats, sharks and crocodiles. We stalked the most fearsome predators in Auckland and talked to the humans who keep them happy - and who would be first on the menu if something went wrong.
"If it's a big animal and it's a carnivorous animal, you have to respect it," says Kelly Tarlton's curator Andrew Christie, who is responsible for the aquarium's shiver of sharks. "You have to keep your wits about you and you have to be professional."
It's been decades since saltwater crocodiles Goldie and Scar killed anything but time. But Butterfly Creek keeper Brian Copland reckons they're just lying in wait.
"He's waiting for the day you really muck up," says Copland about Goldie, a 49-year-old Queensland crocodile who weighs more than half a tonne and is more than five metres long. "You can see it in his eyes."
Of the crocodiles, Goldie is the one Copland trusts more. Scar once had a go at him during a hand-feeding session - "just grabbed the meat and kept coming". No harm done, but since then hands have been off Scar's menu, as far as feeding techniques go.
Trust is a relative concept when it comes to these creatures, who were both born in the wild. Copland and his fellow keepers regularly enter their enclosures armed with just a bamboo pole. They will hand-feed Goldie but they're aware that the crocs have a brain the size of a walnut and there's only one thing on it: survival. If that means devouring the hand that feeds it, then they will.
The keepers have basic rules: never go in the enclosures alone, remain aware of what the crocodiles are doing, watch for changes in behaviour. But a lot of it is instinct and common sense. When Copland has a day off, his chief instruction to his colleagues is: "Don't get eaten. You never take your eyes off him," says Copland, a former dairy farmer from Scotland, as we watch Goldie climb out of his pool. "I'm always a little nervous. You have to be."
Copland says there are no guns at the centre. If a crocodile got someone in a death roll, there wouldn't be time for a keeper to grab a gun - and they would have as much chance of shooting the prey as the crocodile.
If someone was attacked, a keeper would jab the bamboo pole into the crocodile's legs, side or chest in the hope that its instinct to defend itself would overpower its instinct to eat.
They haven't had to test this theory. "I'm confident working with him as long as I can see what he's thinking," Copland says of Goldie.
"And I can see what he's thinking most of the time. If it doesn't feel right, you don't do it. I've got huge respect for crocodiles; these guys amaze me in so many different ways."
Butterfly Creek is open 9.30pm to 5pm daily. Crocodile encounters are at 11am and 2pm. Other predators include tarantulas and alligators. 12 Tom Pearce Drive, near Auckland Airport, ph (09) 275 8880.
Nat Sullivan works with lions every day at Auckland Zoo, yet she has an irrational fear of seals and sea lions. Andrew Murdock works with tigers but shudders at the thought of a tarantula and reckons a Murray cod once almost took his arm off.
Both are certain that should they find themselves stranded with a big cat they would be dead, even if it had known them since birth.
They're confident (but not too confident) that it won't happen. Access to the behind-the-scenes areas is restricted and for the most dangerous areas there's a coveted "lion key" and "tiger key". There's always at least one barrier between a keeper and a big cat. Locks are double checked. Keepers work in pairs. If a big cat was to escape, the police armed offenders squad would be called and the zoo's emergency response team have standard orders to shoot to kill.
Though all the zoo's big cats were born in captivity, its hands-off animal management ethos provides an experience as close to the wild as possible, so they retain their natural instincts. "And their natural instinct, is to kill and eat if they can," says Sullivan. "These animals are as dangerous as it gets."
There are three female lions and one male, Ngala. Sullivan is hoping Ngala will have a chance with the ladies now that the previous dominant male has moved to Australia. The pecking order is likely to change - the girls have picked on Ngala in the past - but Sullivan says they are gentler with each other than you might imagine. "When they do fight it's all noise, it's all arguments. There's very little physical contact. And even if there is, quite often the claws don't come out - they're just hitting with paws.
"It sounds like there's going to be murder but it's all just loud arguing. If you're close enough to them when they roar you can feel it; it goes right through your legs."
One exception to the keeping-things-natural rule is feeding. In the wild, lions would feed according to pecking order. At the zoo they're fed separately to ensure all remain healthy.
Amira, the youngest and most playful of the pride, will also hunt the odd eel that swims into the moat, and stalk wild birds. Sullivan has occasionally had to clear the lions out of the enclosure to rescue or put down an injured duck if the lions haven't finished the job.
The Sumatran tigers - Oz, Molek and their four-year-old cub Birani - also get along pretty well. "These guys are quite relaxed but it's all in the way you handle them," says Murdock, who has scars on his legs from encounters with hand-raised tigers at other zoos.
The keepers try to build a relationship of trust with the tigers, which means, for instance, making a point of being absent when a tiger is tranquillised by a vet, so it doesn't associate the experience with a keeper.
"If you don't work them in the right way, you'll bring out their natural aggressive instincts. The biggest thing I've learned is how quickly things can happen with tigers - how smart they are, and just how seriously you have to take them as an animal. But I love working with these tigers. I love their personalities and I love the fact that they're not always easy going."
Auckland Zoo is open 9.30am to 5.30pm daily. Lion encounters are on Tuesdays and Thursdays at 1.45pm and tiger encounters at 3pm on Saturdays. Other dangerous predators include alligators, cheetahs and tarantulas. Motions Rd, Western Springs, ph (09) 360 3805.
Hamilton Zoo also has Sumatran tigers - as well as painted hunting dogs and cheetahs. Rotorua's Paradise Valley Springs Wildlife Park has lions.
Kelly Tarlton's curator Andrew Christie once found his head inside a shark's mouth. "You're feeding away and sometimes you'll have six or seven sharks coming down and around you. If you're looking at other things you can have a shark come up and give you a wee kiss.
"Usually with the sevengills you'll feel a mouthing before they go in and strike, so you've got a chance to get out of the way. You'll feel the teeth pricking on the neoprene of your wetsuit and you'll know it's time to get the hell out of there. Move your head out of the way, put a fish in its mouth and there's no problem."
About the worst injury an employee has suffered is a cut finger, though there was a morbid encounter a few years ago when a school shark was given a caesarean section one night by a sevengill shark.
The biggest of the 23 sharks are their five sand tiger sharks, which rarely attack humans. The largest of the five measures more than 3m and weighs more than 150kg. The sharks are known by numbers, not names. The big guy is number five. "They're impressive," says Christie. "Sand tigers have a fast jaw reaction and pointy teeth. Their whole jaw can project forward and snap at their food."
The sharks are hand fed twice a week by staff in scuba gear. There are always two divers in the tank, watching out for each other, and an observer is in the shark tunnel. They're careful to angle the food into the sharks' mouths in a certain way and snap their hands away. They'll keep tabs on what shark is approaching, and anticipate its behaviour.
"Each shark behaves in a different way," says Christie. "School sharks will swim around your knees and ankles, and they're a snappy feeder so you have to look out for them. A big female sevengill will swim on by then turn around and come from behind for a feed.
"You'll look out for the danger signs - a faster swimming speed, arching their backs, pointing their petrel fins down. If they're getting really wound up they'll start going in a tighter circle.
"It's not necessarily a threat for us. If a shark has something in his mouth and he's chewing there's nothing to worry about. But you're feeding a respected predator so you have to know what you're doing."
Kelly Tarlton's Sea Life Aquarium reopens on Thursday after a $5 million makeover and change of ownership. Changes include a new walk-through penguin encounter, an upgraded Shark Tunnel and a new interactive rockpool. Open 9.30am to 5.30pm daily. Sharks are fed at 2.30pm Tuesdays and Thursdays, and shark dives and shark cage dives are available. 23 Tamaki Drive, Orakei, ph 0800 80 50 50.