It is hard to believe that Nancy has ingenuity, given that she goes surfing -- alone -- wearing plenty of glittery bling (earrings, necklaces, bracelets, rings).
NOAA Fisheries Service has long offered this advice to recreational water users: "Don't wear shiny jewelry when in the water. The glisten mimics fish scale sheen and visually labels you as shark prey."
The shark in the movie was mostly created via CGI, but Lively told Entertainment Weekly that "they had a guy with a great white sized fin attached and he would swim around on like a little sea doo, like an underwater rocket propeller."
Executive Producer Jaume Collet-Serra teamed with a studio art department for the design of the shark.
"I came to the conclusion that the shark had to be a female," Collet-Serra said. "Females are slightly bigger, and most have great scars from mating. Visually, they're scarier, as they are more protective."
Shark experts disagree.
As Levine said, "Female great whites are definitely not any more protective than males are because their young are precocial and are not protected by their mothers."
Scott E. Anderson, the film's visual effects supervisor, says the shark attacks Nancy early in the movie.
"And after the shark has wounded her, the shark just thinks of Nancy as food," Anderson said.
That may be true of Anderson's fictional shark, but humans are not preferred prey for great whites, which primarily eat marine dwellers such as fish and sea lions.
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While sharks have extremely keen senses and can detect blood from a quarter of a mile away, blood is not necessarily a dinner bell for them.
For example, according to Steve Kajiura of Florida Atlantic University's Shark Lab, there is no evidence that sharks attack menstruating women more than other people.
Lively said that, because the shark was previously hunted by people, "You then understand the shark's motive, his determination, his will, his desperation to conquer as his survival also depends on it."
The shark, which is actually depicted as a female in the film, would likely not act out of anger or revenge. Psychologist Ryan Martin of the University of Wisconsin-Green Bay wrote in his blog, "It's probably unreasonable to say that a shark can feel wronged, unfairly treated, or even have the capacity to blame someone for something."
"The Shallows" does get some things right. Anderson said that the basis of the film's research library consisted of "little moments that Jaume liked" about general actions and behaviors of sharks. There is a seagull in the film that was injured by a shark, and it is true that sharks do at times attack seabirds.
At one point, Nancy estimates the great white's swimming speed. Most experts do believe that sharks can swim 25–35 miles per hour. In another pivotal moment in the film, the shark bites through metal, which has been reported. In yet another scene, the shark leaps out of the water to attack, a move that has also been documented.