Alexandre Aja’s remake of Piranha is, for the most part, tremendous trashy fun. It has no pretensions to be anything other than an unashamed B-movie, with plenty of gratuitous gore and even more gratuitous nudity. I sometimes get depressed by nudity in films – it too often feels like a sop to a perceived audience of teenage boys who don’t get to see the real thing yet, and I feel bad for the actress whose only role in the film is to get her tits out and then get killed. But the nudity in Piranha is so frequent and blatant, so completely over the top that it punches through the barrier of offensiveness to be become almost innocent fun. There are so many breasts on view that after a while you stop noticing them.

But there’s one thing that let the film down for me, and that’s the ending. (Warning: spoilers for Piranha, and several other films, follow.)

Piranha follows what seems to be an increasing number of films in not having a proper ending: it just stops in what is, to all intents and purposes, the middle of a scene. The strategy is to make the audience think the film is over, and the threat has passed, only to pull the rug suddenly out from under them before the end credits crash in. In this case, just as we think our heroes have escaped being eaten by the piranhas, the Basil Exposition character (Christopher Lloyd) rings up to say they were in fact only babies. On cue, a giant – almost mega – adult piranha leaps from the water and swallows the male lead. End of film.

Obviously, twist endings aren’t new. Nor is the habit of horror movies suggesting that the evil has only temporarily been vanquished and will rise again at some indeterminate point in the future – whether that’s revealed by a shot of another baby alligator being flushed into the sewers, or a shot of Freddy Kreuger apparently reflected in a fountain. That’s fine. But with Piranha, we’re left asking – is that the only adult fish? Are all the other characters about to be eaten? Will that include the two children?

This, to my mind, is just bad storytelling; a cheap and lazy trick to play on the audience. It’s not that I object to downbeat endings. Although it’s true that as I get older and more sentimental I prefer at least a ray of hope at the end of a horror movie, sometimes an unhappy ending feels right. Take The Descent, which (at least in the UK) ends with the heroine alone in the caves, lost and apparently mad, as the monsters close in. This felt like the ending to which the film had been building all along; it played fair with the audience. (Shame they couldn’t stick to it; it would have spared us the redundant sequel.) Similarly, the Saw films regularly conclude with a doomed character realising, too late, all the ways they could have avoided becoming one of Jigsaw’s victims.

Piranha’s approach follows any number of other films: the first Friday the 13th, the original Nightmare on Elm Street (a film which famously struggled to get its ending right, and didn’t succeed). Brian de Palma’s Carrie has one of the most famous shock endings, though this is at least revealed to be a dream sequence.

The recent wave of 70s remakes seemingly delight in following the same pattern, so faithfully that you wonder if idiot producers have come to believe it’s a necessary part of the formula. The Hills Have Eyes (also the work of Aja) pulls back to reveal the surviving family members being watched by another mutant, suggesting that their fight isn’t over yet. The recent version of The Crazies pulls pretty much the same trick, though this one asks us to believe the US government is now planning to wipe out an entire city and try to cover it up; I don’t see them pulling that one off. Zack Snyder’s Dawn of the Dead at least has the hope-crushing scenes play out under the end credits, which feels more honest that the “Ha ha! Gotcha!” approach of Piranha.

The Final Destination films love doing this, and one of the reasons that the second is my favourite of the series is that you can still read the ending as having the two lead characters survive. The two following films don’t even bother to pretend there’s any chance of the characters making it to the end, which severely lessens the suspense, and therefore the fun, of the film. The most recent, The Final Destination, is so uninterested in its characters that we learn virtually nothing about them – are they still in High School? College? Gainful careers? Do they have families? Who cares, they’ll all be dead meat in 85 minutes.

Ultimately, this kind of approach cheapens the film. If you want audiences to become involved in your story, however hackneyed it is, they have to care about at least some of the characters and want them to survive. Even a movie like Piranha, which is silly and shallow (that’s not a criticism in context), should take you on an emotional journey with the hero and/or heroine. The audience should feel a degree of empathy. To have that snatched away for the sake of cheap jolt makes a joke of that involvement, as though the filmmakers are mocking you for giving a shit. Hollywood: please stop doing it.