In the movie it is Brody's elder son who ends up in the water with the shark. In the book a teenager goes swimming to win a ten dollar bet and narrowly escapes being eaten. This scene probably also inspired the moment in the film when a fisherman tries to claim the three thousand dollar bounty using a holiday roast and a length of chain and is menaced by what we think is the shark but turns out to be just the tide.
In the book a family drive all the way over from Queens to see the shark. In the movie, Amity is swamped by curiousity seekers with out of state licence plates ("Those aren't my people! They're from all over the place!").
In the book Brody, Hendricks and Hooper make up "the triangle of a watch". The chief patrols the private beach while his deputy keeps an eye on the public beach and Hooper single-handedly covers the ocean in the Flicka. In the movie there are lifeguards, medics, a whole flotilla of shark-spotters, and a coastguard helicopter buzzing the over-crowded coastline.
The filmmakers could have saved a large chunk of their budget ($64 a head for each extra, for starters) by filming the scene that Benchley had written, but they knew that they had to deliver a visual spectacle of mass-panic that an audience fed on a diet of disaster movies had come to expect.
