Brandon, the dive master, is trying to be reassuring, but he's doing a spectacularly bad job of it. "If a shark gets too friendly," he says, "you can push him away with a hand on his nose. But just remember that his nose is here" - Brandon stabs the air with a wetsuit-clad arm, before lowering it slightly - "and his mouth is here. You don't want to get those two mixed up."
No, you don't. There are only a few things I know with certainty about the ocean, and one of them is that you don't want to put your arm in a shark's mouth.
Today, however, it's a possibility. In an hour or so I'll be 20 metres under the water with nothing but a little seaweed-encrusted rope separating me from 30 or so sharks that have come here for lunch.
I'll be doing a shark dive, which to some people might sound about as intelligent as doing a taipan walk, or a cyclone flight.
Why go looking for danger? But the secret is that these marine monsters aren't as vicious as you might think. Ask Brandon how many people have been attacked on shark dives here in Fiji and he'll say, "None. Lately." He's kidding though - the record is clean. Nothing has ever happened.
Of course there's always a first time, and it's hard to reconcile the relative safety of doing this with the sight of 30 large sharks whipping themselves into a feeding frenzy a few metres away from your face. I actually volunteered to do this?
There are reef sharks there in the ocean today. There's also a silver-tip coming in to wrench a fish head away from the guy who has the unenviable job of shark feeder. A few tawny nurses enter the fray. And thanks to the tunnel vision of the diving mask I don't even see the four-metre bull shark until it's gliding past about 30 centimetres from my nose.
You come here seeking adventure, of course, so you can't complain. We're somewhere off the coast of Pacific Harbour, a small Fijian town that has dubbed itself the island nation's "adventure capital". Principal among those adventures is the chance to get up close and salty with one of the ocean's most misunderstood creatures. Actually, with about 30 of the ocean's most misunderstood creatures.
There they are, thrashing around, devouring their fish heads, occasionally fixing the masked sightseers around them with crooked, razor-toothed grins. Most divers rest on their knees, legs and fins tucked below them, hands on the small rope, eyes glued to the amazing sight ahead.
As far as scuba diving goes, it's extreme stuff. The next day is far more sedate - although similarly submerged - as I head out from Pacific Harbour to Beqa Reef.
This is some of the best soft-coral diving in the world, and I'm treated to two leisurely hour-long glides past brightly coloured fan coral, branch coral, coral that looks like clusters of opaque bubbles, sea anemones, and, of course, the anemones' long-time residents, the clown fish.
It's gentle, idyllic, and the perfect way to spend downtime in Pacific Harbour, because tomorrow I'll be ratcheting up the adrenalin once again.
And here we go.
This time I am high up in a tree, in the thick of Fiji's mountain forest canopy. My feet are planted on a steel platform.
My waist is being tugged, gently, as Mike the zip-lining guide threads the clip on my harness into the bracket attached to the wire.
He clicks it into place, then pauses for some quiet reflection. "Isn't it peaceful here Ben?" he asks, sweeping his arm to encompass the jungle, the mountains, the birds, the sky. "Isn't it beautiful?" I nod.
Then I take a deep breath, lean back and all of a sudden I'm flying through the treetops at about 55km/h, dragging a gloved hand on the wire to slow me down before I plough into a tree at the far end. I succeed, just, coming to rest on the next steel platform, the end point of this zip-line, and the starting point of the next one.
This is Zip Fiji, a speedy trip through the treetops just inland from Pacific Harbour.
The experience lasts about 45 minutes as you negotiate nine zip-lines strung high in the air. These shots of adrenalin are interspersed with Mike's quiet reflections on his island's beauty, and the other guide, Ben, egging me on to do a line while hanging upside down.
Like much of Fiji, it's the local characters who make the experience memorable. The same goes the day after when I set off once again from Pacific Harbour in search of adventure.
This time it's whitewater rafting deep in the heart of Viti Levu, remote country only visited by villagers and rafting enthusiasts.
The guides here all come from the local area, they all grew up playing in this river together ... and not much has changed. We're a few hours into the paddle, floating down a deep, calm section of the river, when Moses, a guide from a raft near mine, points up at the trees above us. "You see the fruit bats up there?" he says to me.
I turn to look, scanning the treetops. I can't see anything. All of a sudden there's a yell from behind, a pair of huge Fijian arms wrap themselves around me, and I'm in the water. I surface to find that Moses has leapt across from his boat to drag me into the drink. The guides all laugh, haul me back into a raft and get on with the show.
"Most Fijians have never been here," says Esala, my guide, as he steers us through deep river canyons, past little clusters of houses and over gentle rapids.
Around a rocky bend we see a few people crouched over a fire. One of them turns and sees us, raising a huge eel on a spear above his head, grinning, showing off his catch.
Esala laughs. "There are eels in this river," he says, smiling as the kids on board start to look a bit wary. "Big, big eels."
We all glance down at the murky waters. If he's trying to be reassuring, he's doing a spectacularly bad job of it.
The writer travelled as a guest of Fiji Tourism.
THREE MORE ADVENTURE ACTIVITIES IN FIJI
GAME FISHING Travel just a few nautical miles from Port Denarau and you can be going after marlin, tuna, mahi-mahi, Spanish mackerel and wahoo. Adrenalin Fiji has three vessels and also offers reef fishing and casting for giant trevally. See adrenalinfiji.com.
HORSE-BOARDING You couldn't make this stuff up. Uprising Resort in Pacific Harbour offers guests the chance to go "horse-boarding", which is like wakeboarding, only instead of being towed by a boat you're towed by a horse that runs down the beach. See uprisingbeachresort.com.
JET-SKIING Spend 2.5 hours tearing through the Mamanuca Islands with Adrenalin Fiji's jet-ski safari. The tour includes an island stop-over, plus plenty of time to terrorise the fish from on board your machine; see adrenalinfiji.com.
STAYING THERE Uprising Beach Resort in Pacific Harbour offers villas to beachside bures to dorm rooms. Villas from $FJ335 ($214) night, bures from $FJ255 ($163) and dorm beds from $FJ40 ($25.5). All prices include breakfast. See uprisingbeachresort.com.
SEE + DO The "Ultimate Shark Encounter" with Aqua-Trek US$160 ($191) , including two dives and gear hire; aquatrek.com. Zip Fiji runs the zip-lining; it costs $FJ225 ($143) a person. See zip-fiji.com. For whitewater rafting, Rivers Fiji (riversfiji.com). A day trip costs US$219 ($262) a person.
- Sydney Morning Herald