The shoot was a disaster: way over budget, and with a mechanical shark that kept short-circuiting. But 28-year-old Steven Spielberg (and editor Verna Fields) turned Peter Benchley’s fun beach read into a textbook of cinematic suspense and shock. Seen today, the movie seems a little on the chatty side; the characters aren’t rich enough to justify all that talk. But the first attack, on a solitary nighttime swimmer, packs an undiminished jolt. The shark (which the crew nicknames Bruce) still has an implacable grandeur. And the John Williams theme can be heard, at any seaside resort, when unusual activity is spotted in the water. It’s maritime Morse code for uh-oh.