It’s not hard to scare the willies out of folks with a shark. There may be nothing in the prehistoric part of our brain that tells us to run from zombies, vampires or werewolves. But sharks? We’re wired to be wary of them, and Spielberg just reminded us of that.

Which is why the reactions to most of the Aussies in “The Reef: Stalked” to the great white that is either eating them or bearing down on them for another dinner course are so Actor’s Studio “off.”

As James Lipton might have said, “Sharks are scary. SHOW us that you know this!”

Nope. The ladies on a casual snorkeling/spear-fishing outing to a reef off the coast casually paddle back pretty much as casually as they paddled out.

The most experienced of this quartet, Nic and Jodie (Teressa Liane, Ann Truong) blithely decide to kayak over to a reef island “to get started” on cooking the fish they’ve speared. That leaves “You’re not prepared for this” Annie (Saskia Archer) to relate the fact that she just saw a fin to diving buddy Lisa (Kate Lister).

The “most sharks are timid” lecture falls on deaf ears. Do sharks even have ears? Because that’s when the attacks start.

Writer-director Andrew Traucki’s sequel to his 2010 film “The Reef” has some excellent shark attack footage and manages a couple of passably suspenseful “Jaws” like moments of waiting for the worst to happen.

The best acting moment is a Aboriginal mother frantically summoning first one child, then another, ashore, swimming just off that reef island. She gives us helpless panic, wrenching agony at watching at attack in the offing and then the water turning red.

But nobody else in this picture gives us anything remotely as fearful or real. There’s no panic or even much of a determined, “We’ve got to paddle like hell” to get to shore urgency.

It’s as if that casual dropping of Aussie surfer slang for sharks, “The Man in the Gray Suit,” lulled the four snorkelers to sleep.

La-di-dah, maybe we should do something. Oh bother, our friend just got chomped. Well, let’s see if I/we can save her, or maybe, you know, outthink the insensate beast that’s “hunting us.”

Traucki makes one character a veteran diver traumatized by the fact her sister was murdered by an abusive boyfriend, who drowned her in a tub. But…she “ran off to work a dive boat in Greece” after that murder, and then did a little Eat, Pray Love traveling.

“Water” scares her? Well, I guess it comes and goes. A lot.

Nic is quick to judge couch-potato Annie with “This isn’t you, you can’t do this,” but it’s not like she’s proven good at handling this sort of imminent danger and threat herself.

The best movies like this do a much better job of selling the building terror, the fear of a gruesome injury or death by being eaten alive– drowning in the process. As much responsibility as the writer and director share (they’re one and the same here) in making that primal fear connect with the viewer, it’s the actors who determine whether or not the viewer buys in, empathizes and puts herself or himself in their swim fins, scared half to death.

You don’t have to be Mandy Moore in “47 Meters Down” or Blake Lively in “The Shallows” to be good at mimicking that normal human terror and panic. “Open Water” had a no name cast and yet was shockingly effective at getting across the realization that “We’re dinner if we don’t do everything we can think of, and in a life-or-death hurry.”

Some good shark attack sequences and a simple “Fin!” and “It’s COMING for US” plot doesn’t work because virtually no one at no moment in “The Reef: Stalked” acts as if there’s a bloody shark about to make them the main course.

Rating: unrated, violence, profanity

Cast: Teressa Liane, Ann Truong, Saskia Archer, Kate Lister

Credits: Scripted and directed by Andrew Traucki. An RLJE Entertaintment/Shudder release.

Running time: 1:31