And some of the meat is just plain weird, all alien and hungry and horny to turn those of us it doesn’t eat into breeding machines for more of itself. This is really quite freakin’ disturbing and employs some deeply unsettling rape imagery that you might expect more from a female filmmaker -- writer/director James Gunn is making his feature directorial debut here; he wrote the brilliant 2004 update of Dawn of the Dead -- along with some deeply unsettling behold-the-reproductive-power-of-woman-that-scares-us-guys-no-end stuff that we’re used to seeing from male filmmakers: the Alien films, fer instance. I guess you could call Slither an equal-opportunity skin-crawler. And it is the best oh-my-god-get-it-OUT-of-me bodily-invasion film since Aliens.

But here’s the deeply astonishing thing about Slither: at the same time that it’s making you want to scratch your own skin off, it’s also really funny, in a grim black way, and full of hilarious little touches that humanize the characters in a manner that’s all too rare for horror. Which in turn makes the horror even more horrific, actually, and more poignant. You somehow need to genuinely root even harder for a small-town sheriff, like Nathan Fillion’s (Serenity) Bill Pardy here, when he’s the kind of man who takes his hat off when he talks to a lady, even after she’s been transmogrified into a huge and hideous alien breeding colony.

There’s a strange and pleasant kind of sweetness to the people of the small town of Wheelsy, a throwback-edness that reminds you of the folks in all those 1950s movies about body-snatching invaders and giant ants. It’s meant to -- Slither is an homage to those films as much as it is to the shocking horror films of the 70s. But it’s not that they’re not entirely modern, either, or way more complex and way less predictable than you imagine going in. Fillion is perfectly deadpan delivering Pardy’s totally contemporary snark, but thoroughly engaging, too, with Pardy’s longtime torch-carrying for schoolteacher Starla Grant. Starla (Elizabeth Banks: The 40 Year-Old Virgin, Spider-Man 2) has lots of of-the-moment spunk, but her devotion to her husband, Grant (Michael Rooker: Undisputed, The Bone Collector) -- yes, that makes his full name Grant Grant -- is sincere, even after he turns into a monstrous squidlike extraterrestrial creature bent on the anihilation of planet Earth. It kinda makes you wanna laugh and cry at the same time you’re also trying to scratch your own skin off.

But some small-town values don’t escape scorn, on the other hand, like how everyone seems to know your business and be talking about it down on Main Street. Sheriff Bill’s got one deliciously snide and blunt comeback to a deputy who knows too much and brings it up at inappropriate moments, but it’s Starla who has the best and more, um, visceral revenge when it starts to appear that everyone who’s been infected by the little slugs borne of Grant and the invading alien appear to know everything Grant knew, including intimate details of their marriage. Anyone who’s had to face unpleasant gossip will surely appreciate her solution.

It’s not often that a horror flick comes around that’s this outrageous, this gonzo... and also this warm and good-natured and even kinda touching. In fact, it might have never happened before.