Though the last few years have seen a gradual return to harder and more violent horror movies after about a decade of feeble, teen-friendly thrillers, it's still hard to be prepared for Piranha 3D, directed by French gorehound Alexandre Aja, from a screenplay by Pete Goldfinger & Josh Stolberg. This is not a film that should ever have made it into a mainstream multiplex; its genes were formed in the warm, wet pool of the '70s grind house, when exploitation films didn't just feature nudity and blood, they featured fucking and graphic evisceration. Naturally enough, I adored every second of it, all the more because in addition to be wanton and filthy and foul, it's absolutely as tacky as hell.

Its title, for God's sake, is Piranha 3D (or actually, not: onscreen, it's just Piranha. But you know what I'm aiming at). And a tawdrier display of the possibilities of 3-D projection has not been seen anywhere in the three-year lifespan of the current phase of that fad, though the "eyeball on a pick-axe" scene in My Bloody Valentine 3D is coming from the same place. Piranha 3D is a whole feature's worth of eyeballs on pick-axes: limbs, toothy fishes, geysers of blood, and lots of naked female breasts jut straight out at the audience with mercenary abandon. "Tawdry", did I say? It's downright indecent.

Not really remaking 1978's Piranha, a horror-comedy masterpiece directed by Joe Dante and written by John Sayles, so much as agreeing with its notion that it might fun to throw a hell of a lot of carnivorous fish at a waterside resort, Piranha 3D presents us with Lake Victoria, Nevada, one of those little communities whose economy depends entirely upon one brief tourist season. The kind where e.g. if you had to shut down the local tourism site e.g. a beach, it would destroy the lives of every regular citizen.

So it's spring break, and Sheriff Julie Forester (Elisabeth Shue, gamely adding a sense of character to a largely functional role) is busy dealing with the hordes of screaming college students, while she things her eldest son, Jake (Steven R. McQueen) is babysitting his siblings Laura and Zane (Brooklynn Proulx and Sage Ryan). In actuality, Jake is torn between doing his noble duty, fecklessly pursuing his old high-school crush Kelly (Jessica Szohr), and following the hypnotically sleazy producer of a Girls Gone Wild knock-off, Derrick Jones (Jerry O'Connell), on his quest to film naked drunk girls cavorting in the quieter parts of the lake. More to the point, an underlake earthquake has just opened up a cavern that has been isolated for thousands of years or more, releasing a bunch of big goddamn piranha. You have more than enough to go on - everything before "big goddamn piranha" is window dressing, and the film knows it.

The film, in fact, knows many things. Its predecessor was one of the first meta-horror films, both serious in its intent to terrify and thrill, and also a loving satire of its own kin. Funny as hell when it needed to be, but never a spoof, always a real honest-to-God killer animal movie; that was Piranha. Now, Piranha 3D attempts to do the exact same thing, and it is not as successful - trading in the writer of Lone Star for the writer of Good Luck Chuck will have that effect - but it is altogether more successful than a hard-R horror movie in 2010 has any right to be.

We get the sense at the word "go" that Piranha 3D has a certain cleverness to it when the film opens on a shot of a man sitting in a boat, singing drunkenly while he fishes. The man is played by Richard Dreyfuss, and the song is "Show Me the Way to Go Home", and the movie does not insist, at all, that we understand why this is significant. The scene could play just as easily as a random, inexplicable Richard Dreyfuss cameo that sets up the plot, but if you know that Jaws exists - and anyone seeing Piranha 3D probably knows this - it's a clear, unashamed admission by the filmmakers: "Oh, yeah, we are going to rip-off Jaws something fierce, by the way".

For every moment that follows, it's absolutely clear that Aja and his crew are making a movie that they know very well is derivative, hackish, and cheesy: they count on it. One can say anything about Aja - beginning with the fact that every one of his features suffers from some crippling flaw or another - but he's a smart director, who knows how to play the audience like nobody's business. And, as he now proves for the first time ever, a director with quite a broad sense of humor.

Piranha 3D is not, emphatically, a deconstructionist work, along the lines of Scream or (arguably) Aja's own High Tension. There is no meaningful sense in which it subverts it own existence or tries to apologise for its own wildly poor taste and leering sexism. At the same time, it's profoundly self-aware (that Jaws> gag, for example), and throughout all the trashy exploitation, it feels like there are in a sense two different movies going on at once: the obvious neo-grind house picture, in which naked boobs and buckets of fake blood are thrown out just because those things are awesome, and a slightly sheepish, mostly pleased movie that keeps remarking to itself: "well, this is the kind of movie where there ought to be a lot of naked women, so here they are. Tits ahoy!" In other words, the film is fully aware that it belongs to a certain kind of extraordinarily crass genre without feeling the need to distance itself from that genre. The exact opposite, in fact: one of the most immediately notable facts about Piranha 3D is its 110% commitment to being trashy, whether it's a parasailing scene that appears to have been placed in the movie solely to afford the shot of a topless woman flying towards the camera, or an extended - very extended, long beyond what I'd have assumed remotely plausible - sequence in which seemingly hundreds of extras are killed off in ways that far outstrip anything even in Aja's notably bloody oeuvre. One could argue that the excessiveness of all these sequences is by its nature self-parody; and certainly, you'd need to be clinically dead not to understand how a scene of two women making out underwater for several minutes, set to LΓ©o Delibes's "Flower Duet" from LakmΓ© is clearly meant to be a joke, even if it's not right up your alley. And certain elements, such as O'Connell's boisterously slimy performance as a Joe Francis clone (the filmmakers' game attempt to prove that they're not just interested in ogling women; they're equally anxious to punish the ultra-male chauvinist in the most humiliating gag possible), or Christopher Lloyd's showstopping cameo as a demented ichthyologist, or the deliberately stupid final shot, can only be regarded as farce. On the other hand, the most outrΓ© gore effects (which I should not even imagine giving away) are far too seriously sick to be funny, even if they are immensely delightful.

At one point, Laura humiliates her older brother by explaining, at great length, that he enjoys looking at boobs. This odd little moment, clearly motivated by the evergreen love of putting precocious little girls into films, has a double function; subsitute "the audience" for "Jake", and she is essentially mouthing Piranha 3D's manifesto. We are here to see exploitative junk, and Aja has the respect for the audience and the integrity as a horror director to give us exploitation, with none of the sadism of a Saw and none of the fainting-couch niceness of a PG-13 slasher flick.

One has the clear sense that everybody involved is very proud of Piranha 3D, right down to its damnably shoddy post-conversion to 3-D (it was always meant to be in 3-D, however, unlike other post-converted films). There is a story that, upon seeing the desperately fake-looking robin at the end of Blue Velvet, the shame of that film's effects crew, David Lynch was ecstatic almost beyond words. So it is, I suspect, with the cheap 3-D here: it adds to the sense that we're watching something too unbelievably crass to live, and wonderful because of it. So praise to you all, makers of Piranha 3D! To you, Aja, and to you, cinematographer John R. Leonetti, and to you, editor who is named only Baxter, and the wonderful make-up people at K.N.B. EFX: you have made a movie that is slick and shallow and nasty in every way, and I enjoyed it more than I would have imagined possible.