The opening scene from the 1975 Steven Spielberg film Jaws was shot over three days at South Beach Edgartown on the Massachusetts island, Martha's Vineyard which sits just south of Cape Cod.
The scene itself starred Susan Backlinie who played Chrissie Watkins and took three days to shoot. The first batch of shots taken by Spielberg didn't produce what he was looking for. He felt the reaction Backlinie was giving wasn't real enough. That's why when they returned to shooting Spielberg decided not to tell Backlinie when the shark was going to attack. When the underwater diver grabbed and pulled at her leg, Backlinie had no idea it was going to happen and her reaction was real. This was the shot that made it into the final film.
Richard Dreyfuss who starred as Matt Hooper said that this scene truly terrified him.