Much like the shark itself, the movie starts slowly, deep down in the depths before coming to the surface to explode in pure sensationalism.
Jaws is one of those rare exceptions where high-brow art meets fun entertainment. At the time of its making, however, simply keeping its head above water was the most the cast and crew were hoping for.
But Spielberg had created something special. During production, no one saw it--I'm not sure Spielberg himself saw it, but it was there. I think it was really editor Verna Fields who saw it and put it together.
Jaws begins the way most primal fears begin: someone is alone, in the dark, in an alien environment, and is being attacked from some unknown entity. People remark today how Jaws worked so well, that it's kept them afraid of the ocean for years. I disagree. I think it's because we are scared of the ocean is why Jaws works so well. The opening scene of the young girl being savaged in the black nothingness that is the night ocean is terrifying because it preys on primal fears; it doesn't create them.
Next we're introduced to our cast of characters: There's Police Chief Martin Brody--an everyman with a fear of the water--and his wife, Ellen. There's Brody's loyal deputy Len Hendricks (mysteriously named "Jeff" in the sequel). Then, of course, there's the other side. There is the crooked mayor Larry Vaughan, and his two toadies newspaper editor Harry Meadows and coroner Carl Santos. After Brody and Hendricks find evidence of a hungry shark off the coast of the resort town of Amity, they do the sensible thing and start closing up the beaches. The mayor, seeing dwindling dollar signs, convinces Meadows and Santos to back him, and together they confront Brody and put the kibosh on his beach closing plan.
In an era where the primitive special effects technology gave us a shark that looked like a pool toy, it became essential that the shark not be the focal point of the film. And while a fin here and a barrel there do work wonders, it's only because the shark is far from the only villain in the movie. To have credibility, we have to have a human villain. And that is where Vaughan comes in.
After Vaughan's cavalier "it-can't-happen-again" attitude blows up in his face, Brody brings in the book smart, but decidedly out-of-his-element marine biologist Matt Hooper. Hooper tells Brody everything he and we, the audience, already know: The shark is out there; it's hungry; it's eating people; and it will continue to do so unless it is killed.
After a disastrous Fourth of July celebration that should have gotten Vaughan impeached, Brody and Hooper join forces with Quint, a grizzled fisherman with a personal vendetta against sharks. The movie then switches from its horror and drama elements and becomes something of an adventure, foreshadowing Spielberg's work on films like Raiders of the Lost Ark. Even John Williams' score begins to conjure up images of Errol Flynn-style swashbuckling. The adventure almost seems fun.
And that is when the shark, previously only a shadow, fin, or plot point referenced by dialogue, takes center stage. The movie shifts gears further near the end, going from adventure to a full on monster movie.
The build up is slow, relying on showing us the results of the shark's presence rather than the shark itself. This creates enough fear and credibility so that by the time the big, rubbery toy shark is commanding the screen, we're afraid of it. It's already been established as a monster.
The movie's pacing, dialogue and acting are all perfect, creating a strong enough foundation on which a silly, albeit terrifying, plot rests. By the time the shark is sinking boats and eating shark cages, Spielberg has made us by into it that he could have had the shark blasting off for the moon and we would have accepted it. And that is how and why Jaws works.