Daah dun, daah dun, daah dun, dun dun, dun dun, dun dun. On June 20, 1975, Steven Spielberg’s Jaws—the original summer blockbuster—arrived in theaters and scared moviegoers out of the water. Here are 25 things you might not have known about the Oscar-winning shark flick.

1. Peter Benchley's book Jaws could have been called something else.

Jaws is adapted from author Peter Benchley’s bestselling novel of the same name, which Benchley based on a series of shark attacks that occurred off the coast of New Jersey in 1916 and after an incident where a New York fisherman named Frank Mundus caught a 4500-pound shark off the coast of Montauk in 1964. Other title ideas Benchley had before settling on Jaws were “The Stillness in the Water,” “The Silence of the Deep,” “Leviathan Rising,” and “The Jaws of Death."

2. Peter Benchley makes a cameo in Jaws.

Peter Benchley makes a cameo in Jaws (1975). MCA/Universal Home Video

Benchley himself can be seen in a cameo in the film as the news reporter who addresses the camera on the beach. Benchley had previously worked as a news reporter for The Washington Post before penning Jaws.

Steven Spielberg also makes a cameo in the movie: His voice is the Amity Island dispatcher who calls Quint’s boat, the Orca, with Sheriff Brody’s wife on the line.

3. Steven Spielberg got the directing job on Jaws because of Duel.

Spielberg was chosen to direct Jaws by producers Richard Zanuck and David Brown (who had also worked with the then-28-year-old director on his 1974 film The Sugarland Express) because of his film Duel, which featured a maniacal trucker terrorizing a mild-mannered driver. The producers thought the movie was thematically similar to the story for Jaws, making Spielberg a great fit.

4. THERE’S NOT A LOT OF JAWS IN JAWS.

The shark doesn’t fully appear in a shot until 1 hour and 21 minutes into the two-hour film. The reason it isn’t shown is because the mechanical shark that was built rarely worked during filming, so Spielberg had to create inventive ways (like Quint’s yellow barrels) to shoot around the non-functional shark.

5. Jaws took a very long time to make.

Jaws was marred with so many technical problems (including the shark not working and shooting in the Atlantic Ocean) that the originally scheduled 65-day shoot ballooned into 159 days, not counting post-production.

6. Jaws's Amity Island was actually Martha's Vineyard.

To create the fictional town of Amity, the production shot on location in Edgartown and Menemsha on Martha’s Vineyard in Massachusetts. Strict land ordinances kept the production from building anywhere—Quint’s shack was the one and only set built for the movie, while the defaced Amity Island billboard had to be constructed and taken down all in one day.

7. The shark in Jaws weighed more than a ton.

Roy Scheider in Steven Spielberg's Jaws (1975). MCA/Universal Home Video

The pneumatically-powered shark, designed and built by production designer Joe Alves, weighed in at 1.2 tons and measured 25 feet in length. Part of the reason that Martha’s Vineyard was chosen as a location was because the surrounding ocean bed had a depth of 35 feet for up to 12 miles offshore, which was perfect for scenes that required the mechanical shark rig to be rested on the shallow ocean floor.

8. Steven Spielberg took inspiration for Jaws from his legal counsel.

The director nicknamed the shark “Bruce” after his lawyer, Bruce Ramer, who also currently represents other celebrities like Demi Moore, Ben Stiller, and Clint Eastwood.

9. Some good, old-fashioned elbow grease helped create Jaws's opening scene.

The opening scene took three days to shoot. To achieve the jolting motions of the shark attacking the swimmer in the opening sequence, a harness with cables was attached to actress Susan Backlinie’s legs and was pulled by crewmembers back and forth along the shoreline. Spielberg told the crew not to let Backlinie know when she would be yanked back and forth, so her terrified reaction is genuine.

Spielberg went on to spoof his own opening scene for Jaws in his 1979 World War II comedy 1941. The scene features Backlinie once again taking a skinny dip at the beach, but instead of being attacked by a shark she’s scooped up by a passing Japanese submarine.

10. Roy Scheider landed the lead role in Jaws with a little bit of eavesdropping.

Scheider got the part of Chief Martin Brody after overhearing Spielberg talking to a friend at a Hollywood party about the scene where the shark leaps out of the water and onto Quint’s boat. Scheider was instantly enthralled, and asked Spielberg if he could be in the film. Spielberg loved Scheider from his role in The French Connection, and later offered the actor the part.

11. Richard Dreyfuss wasn't the first choice to play Hooper in Jaws.

Spielberg initially approached Jon Voight, Timothy Bottoms, and Jeff Bridges to play oceanographer Matt Hooper. When none of them could commit to the role, Spielberg’s friend George Lucas suggested Richard Dreyfuss, whom Lucas has directed in American Graffiti. Dreyfuss would later accept the part because he thought he was terrible in the title role of the film The Apprenticeship of Duddy Kravitz a year earlier.

12. Robert Shaw wasn't the first choice to play Quint in Jaws.

When actors Lee Marvin and Sterling Hayden—the first and second choices to play the grizzled fisherman Quint, respectively—both turned Spielberg down, producers Zanuck and Brown recommended English actor Robert Shaw, whom they had previously worked with on 1973's The Sting.

13. A Martha's Vineyard fisherman was the real Quint.

Shaw based his performance of Quint on Martha’s Vineyard native and fisherman Craig Kingsbury, a non-actor who appears in the film as Ben Gardner. Kingsbury helped Shaw with his accent and allegedly told Shaw old sea stories that the actor incorporated into his improvised dialogue as Quint.

14. Gregory Peck forced a scene to be cut from Jaws.

In early drafts of the screenplay, Quint was originally introduced while causing a disturbance in a movie theater while watching John Huston’s 1958 adaptation of Moby Dick. The scene was shot, but actor Gregory Peck—who plays Captain Ahab in that movie—owned the rights to the film version of Moby Dick and wouldn’t let the filmmakers on Jaws use the footage, so the sequence was cut.

15. The book version of Jaws was very different from the movie.

Early drafts of the screenplay featured a subplot where Hooper has an affair with Chief Brody’s wife, which was carted over from the book. Another detail left out of the movie from the book was that Mayor Vaughn was under pressure from the mafia, not local business owners, to keep Amity’s beaches open because of their real estate investments on the island.

16. Steven Spielberg added an offscreen improv moment to Jaws.

The scene where Brody’s son Sean mimics his father’s movements at the dinner table was based on a real thing that happened between Scheider and child actor Jay Mello in between takes. Spielberg loved the off-the-cuff moment so much that he re-staged it and put it in the movie.

Another iconic moment was also a spontaneous one: Brody’s famous “You’re gonna need a bigger boat” line was entirely improvised by Scheider on the day of shooting—and based on an inside joke within the production.

17. Robert Shaw put his on spin on the U.S.S. Indianapolis speech.

MCA/Universal Home Video

Quint’s U.S.S. Indianapolis speech wasn’t in the novel, and the backstory of Quint being a sailor on the ship first appeared in an uncredited rewrite of the script by playwright Howard Sackler. Later, writer-director (and Spielberg’s friend) John Milius expanded the characteristic into a multi-page monologue, which was then whittled down and spruced up by actor Robert Shaw (himself a playwright) on the day of shooting.

18. Some of what you see in Jaws is real shark footage.

Zanuck demanded that real shark footage be used in the movie, and Spielberg used it sparingly. He hired experts Ron and Valerie Taylor to shoot underwater footage of 14-foot sharks off the coast of Australia. For scale, they hired a little person actor named Carl Rizzo to appear as Hooper in a mini shark cage in hopes that they could create the illusion of a shark attacking the character. After trying to get the right shot for about a week, the sharks would only swim around the cage. Then, during a take when Rizzo wasn’t in the cage, a shark became entangled in the cage’s bridle, causing it to thrash and roll around. This footage was included in the final film.

19. Despite all the bloody shark attacks in Jaws, the movie is rated PG.

Jaws was initially rated R by the MPAA. But after some of the more gruesome frames of the shot showing the severed leg of the man attacked by the shark in the estuary were trimmed down, the film was given a PG-rating (the PG-13-rating wasn’t created until after Spielberg’s own film, Indiana Jones and the Temple of Doom, caused the MPAA to change the system in 1984). The poster for the film still reads that the movie “MAY BE TOO INTENSE FOR YOUNGER CHILDREN.”

20. Steven Spielberg didn't direct some of Jaws's final scenes.

Spielberg didn’t direct the shot of the shark exploding. In fact, he had already returned to Los Angeles to begin post-production on the film after the film’s grueling shooting schedule and left the shot up to the production’s second unit.

21. Jaws's poster image came about by chance.

The film’s iconic poster image was designed by artist Roger Kastel for the paperback edition of Benchley’s book. Kastel modeled the image of the massive shark emerging from the bottom of the frame after a great white shark diorama at the American Museum of Natural History. The female swimmer at the top was actually a model that Kastel was sketching at his studio for an ad in Good Housekeeping. He asked her to stay an extra half-hour and had her pose for the image by standing on a stool and pretending to swim.

22. Jaws was the biggest hit Hollywood had ever seen.

Jaws was the first movie released in more than 400 theaters in the United States, and the first movie to gross over $100 million at the box office. It was the highest grossing movie of all time until Star Wars was released two years later.

23. Steven Spielberg included a nod to his previous movie in Jaws.

The faint roaring sound that is heard after the shark is blown up was also used by Spielberg in Duel, when that film’s villainous truck falls off a cliff.

24. Jaws originally ended in the same way as Moby-Dick.

The original ending in the script had the shark dying of harpoon injuries inflicted by Quint and Brody à la Moby Dick, but Spielberg thought the movie needed a crowd-pleasing finale and came up with the exploding tank as seen in the final film. The dialogue and foreshadowing of the tank were then dropped in as they shot the movie.

25. Jaws's main theme music is easy to play.

The sole music notes played for composer John Williams’s Jaws theme are E and F. Jaws marked the second time Williams worked with Spielberg after his film The Sugarland Express, and Williams has composed the music for every Spielberg movie since with the exception of 1985's The Color Purple and 2015's Bridge of Spies.

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