It happened today - June 20, 2015 Well, that bites. On this day in 1975 Jaws was released and it was never safe to go back in the water again. Seriously. Some people have never recovered from that film when it comes to the vexed scientific question whether the Caribbean is ¾ salt water and ¼ ferocious shark. I know. I married one.

The highest-grossing movie in U.S. history until Star Wars came along (a story for another day) it really was an instant classic. Unlike the sequels.

Now what’s remarkable is that when it comes to special effects… OK, ordinary effects… Jaws is a bit lame. “Bruce” the mechanical shark was so unrealistic they had to revamp the movie to focus more on the hidden menace of the beast than on something swimming in a straight line like a fiberglass boat rather than exhibiting the lithe sinister side-to-side motion of a shark. Of course it’s easier to forgive clunky special effects in a pre-Star Wars movie. But it’s also clear that while cool special effects are, well, cool, they’re not central to a great film.

Obviously the movie spoke to people’s deepest fears. But it spoke in a convincing way. And as must happen to achieve cinema greatness, it turned on the individual performances and even more on the way they work together. Roy Scheider and Richard Dreyfuss are a perfect odd couple and Robert Shaw the perfect foil. (Can you believe he’s the same guy who played the villain in From Russia With Love? It must be odd to be an actor who excels at playing out-of-control characters). I’m not sold on the mayor, a cardboard cutout, but the big three are superb.

Incidentally, I’ve always loved the scene where Scheider’s working-class stiff cop Martin Brody discovers that Dreyfuss’s Matt Hooper has his own boat and research gear. I was going to quote from memory because IMDB unaccountably doesn’t have it in their memorable quotes but I found a plausible version online: “You rich?” Brody asks, “Yeah,” Hooper replies tersely. “How much?” “Personally or the whole family?” I think that exchange all by itself settles the apparently apocryphal but memorable exchange between F. Scott Fitzgerald (“The rich are different from you and me”) and Ernest Hemingway (“Yes, they have more money”) in favour of Fitzgerald. A rich person has a different life. They have a larger wake, though it doesn’t make them happier or better. Or more shark-proof.

Speaking of which, IMDB does have their classic final exchange: “I used to hate the water...” “I can't imagine why.” And some people didn’t use to until they saw the film and now, four decades on, they still do. It’s the mark of a great movie that it can change your life, even with a fiberglass shark.