The last eight or so pages of the book are rife with details that, in some form or other, would we woven into the movie. The lines that connect text and film are so snarled and knotted that you need more than a knowledge of basic seamanship to untangle them. The shark's sudden appearance at the stern while Brody is chumming is one of the movie's big scares, and it has its origins in the text:
"Suddenly he saw the monstrous head of the fish [...] black eyes staring at him, silver-gray snout pointing at him, gaping jaw grinning at him. "Oh God!" Brody said, wondering in his shock how long the fish had been there before he had stood up and turned around."
The shark attacks the boat, first by chewing on the transom, and then ramming the hull from below ("The boat shuddered again, and there was a dull, hollow thump.") It is exactly the sound of "a dull, hollow thump" that in the movie interrupts the drunken sailors' chorus of 'Show Me The Way To Go Home'. Quint manages to get an iron in the shark (hitting it at more or less the same spot as in the film), and the first barrel pops off the transom. Almost immediately afterwards, the shark leaps out of the water and obligingly exposes its "smoke-white belly" to Quint's second iron. In the movie Quint's second harpoon pierces the shark's flank, and it is with his third shot that he finds a target in the white skin below the fish's jaw. In the book Quint gets the shark in the head - "over the right eye" - with his third iron. Whether intentional or not, the number of irons has a suggestion of religious symbolism: the devil fish is vanquished by a trinity.
Leaping out of the water in pursuit of its prey is normal hunting behaviour for a Great White, but the limitations of the mechanical shark would not allow Spielberg to include it in his movie. Indeed, the sled-shark proved to be so uncooperative that the director was forced to rethink his approach and roll out the barrels. The idea had been there in the book all along: "Following the boat, keeping pace, were the two red wooden barrels."
The decision to change the colour of the barrels in the movie was informed by the director's wish to avoid red except for blood (the one exception being the estuary victim's rowing boat), and by an overall colour scheme that made yellow - from the curtains in the Brody kitchen, through the sun hat worn by Mrs Kintner, to the underwater lights on Hooper's boat - a queasy visual indicator of the shark that threatens to eclipse Amity's sunshine ("A cloud in the shape of a killer shark.").
In the book the shark chases the Orca ("The barrels kept coming, plowing through the water...") and Brody asks Quint, "Have you ever had a fish do this before?" - a line which Hooper delivers in the film. Quint's remark that "no normal fish can sound with three irons in him and three barrels to hold him up" also makes it into the movie, albeit in a slightly terser form ("He can't stay down with three barrels on him. Not with three barrels, he can't.").
The Orca begins taking on water, but Quint seems unconcerned ("He's banged us up, all right, but the pumps should take care of it.") and sticks with his plan to tow the shark in once it has drowned. There then follows a paragraph that describes the movement of the barrels "on a random path across the surface of the sea", and over those four sentences three long hours pass. Film, being by its very nature a kinetic medium, could not slow down the chase once it had begun.
As Quint and Brody wait for the shark to tire itself out, the rain eases off, though the sky remains "an unbroken sheet of gray." Quint makes a noose to throw around the fish's tail when it surfaces. Once lassoed he intends to "drag him till he drowns". The fisherman uses a similar tactic in the movie ("Draw him in to the shallow water. Going to draw him in and drown him."), but - as Shaw's delivery of the line implies - it is not so much a plan as an act of desperation. To throw a rope around the shark's tail, Quint must bring the fish to the surface. He snags a rope attached to one of the barrels using a gaff - a task that in the movie he gives to Hooper and Brody ("Alright, gentlemen, snag 'em.") - and then runs the rope through a pulley. He uses a winch to pull the shark up, a machine that in the film would be used to lower the shark cage into the water.
In both book and film the action of the winch is interrupted by the shark leaping out of the water and landing on the Orca's stern. Benchley's description of the moment is freighted with religious symbolism, the shark rising up like one of William Blake's dark angels:
"The fish broke water right beside the boat, with a great rushing whoosh of noise. It rose vertically, and in an instant of horror Brody gasped at the size of the body. Towering overhead, it blocked out the light. The pectoral fins hovered like wings, stiff and straight, and as the fish fell forward, they seemed to be reaching out to Brody."
This was the very scene that Roy Scheider overhead Spielberg describing to a guest at the Hollywood party where, according to Jaws legend, he was cast as Amity Chief of Police, and the same scene that made even veteran producer David Brown doubt the wisdom of snapping up the rights to the novel.
