You need to watch the most gonzo sci-fi movie on Amazon Prime ASAP

James Gunn is more twisted than you might realize.

Long before making his mark on mainstream superhero cinema with Marvel’s Guardians of the Galaxy films — which hold up, by the way, as that franchise’s most nutty, endearing entries — the filmmaker got his start at Troma Entertainment, studying under schlock-horror tycoon Lloyd Kaufman.

It was at Troma that Gunn learned how to channel the outsider ethos and gloopy excess of ‘50s B-movies. There, he picked up many of the same farcical, splatter-filled filmmaking techniques he’d later work into everything from 2004’s Scooby-Doo 2: Monsters Unleashed to this summer’s The Suicide Squad.

But before crossing over into the big leagues, Gunn took what he’d learned at Troma and made his directorial debut back in 2006 with Slither, an underrated sci-fi horror comedy that perfectly crystallizes the very brand of “gooey sentimentality” that’s since become his calling card.

Though Slither was financially unsuccessful during its theatrical run, it’s since become something of a cult object. Now that the film is streaming on Amazon Prime, here’s why you need to add it to your midnight-movie must-list.

Slither opens in the time-honored tradition of alien-invasion pictures such as 1958’s The Blob (a personal favorite of Gunn’s), as a swarm of extraterrestrial slugs makes its way to Earth via a meteorite. Crash-landing in the vicinity of Wheelsy, a sleepy South Carolina town, these slimy parasites set about infecting the local residents, starting with wealthy homeowner Grant (Michael Rooker).

Taking over his body as they assimilate his mind, the slugs mutate Grant into an absurdly hideous man-monster, his limbs warping into fleshily elongated whips. He’s not the only townie transformed by the “squirms,” which also wriggle into local woman Brenda (Brenda James) after Grant abducts her to serve as a breeder for thousands of alien larvae. (Slither’s reveal of Brenda’s fate, as she’s bloated beyond recognition to accommodate these parasites, is one of its most jaw-droppingly gross moments.)

But if you can stomach it, Slither is a sweeter-natured film than all its tongue-in-cheek grotesqueries suggest. Racing after Grant in an effort to halt his transformation is his wife Starla (Elizabeth Banks), who grows suspicious of her husband’s erratic behavior. Eventually, we learn slugs have absorbed Grant’s love for Starla, causing him to hide the truth from her and establishing Slither as a squeamish sort of doomed romance.

Also on full display through this storyline is Gunn’s ability to select the perfect needle-drop for every occasion, which has since made him Hollywood’s go-to guy for retro-earworm mix-tapes. Air Supply’s “Every Woman in the World” is employed to a particularly memorable effect.

But between the glorious role played by a zombified deer and an earnest debate over the term “Martians” (does it encompass all extraterrestrial invaders, or should it be reserved for those actually from Mars?), Slither is also decidedly comedic. Nathan Fillion brings deadpan zest to hapless police chief Bill Pardy. Gregg Henry is even more delightful as Jack MacReady, the jumpy, foul-mouthed mayor of Wheelsy, who captures Slither’s broad-grinning madness with one-liners like, “If I weren't about to shit in my pants right now, I'd be fuckin' fascinated.”

What makes Slither such a romp, in addition to these well-calibrated performances, is its buckets of blood are carried off with reverence for B-horror classics and deep cuts alike. Slither is bursting at the seams with Easter eggs.

Wheelsy’s Earl Bassett High is named for Fred Ward’s character in Tremors, while Henry’s MacReady is a hat-tip to Kurt Russell’s MacReady in The Thing. Gunn’s repeatedly stated that Slither owes a sizable debt to the stickier body-horror freakouts made by David Cronenberg, especially Shivers (1975), Rabid (1977), and The Brood (1979).

The influence of Shivers hangs heaviest over Slither; some images are recreated directly, like the one in which Barbara Steele’s bath is disrupted by a parasite, its bulbous head gradually floating up between her legs. (In Slither, actress Tania Saulnier is the unlucky young woman on the receiving end of one pesky parasite.) Both films are more broadly linked by the sincerity with which their directors approach such ludicrous narratives.

Missing from Gunn’s Slither is the more exploitative, leering side of Shivers, which drew a sick charge from turning its high-rise of yuppies into sex-crazed zombies. Instead, Gunn’s film is a softer-hearted B-movie, too much of a loving homage to be morally repulsive beyond the visual. In this way, Slither clarifies what Marvel might have seen in Gunn all those years ago; the ratio of sci-fi horror to comedy is surprisingly even, and the filmmaker toggles between them with a showman’s grace.

Gunn, speaking to Chud around the film’s theatrical release, expounded upon this tonal balance in a way that makes Slither feel like a skeleton key:

“I think the line between creepy and funny is very thin. Creepy can be funny, and funny can be creepy. I also think that one of the things we tried to do was have the actors play it straight, so they’re reacting to everything as if it was real. And because it’s so absurd that’s exactly what makes it funny and that’s also what makes it scary — they’re treating it real and at the same time it’s ridiculous when Starla is talking to her deformed husband out in the field, telling him that maybe he can get a little help and he’ll be OK. Like there’s some ointment that will clear up the fact that he’s a giant slug.”

Watching The Suicide Squad, with its gory yet warm-hearted ode to DC’s most notorious antiheroes, it’s clear Gunn feels such an enduring affinity with found families and the power of love. Emptily reveling in gore has never appealed to him.

And Slither, even with its squeamish practical effects and escalating body count, never really stops being a story about a marriage in crisis. As portrayed by Banks, Starla is truly moving in her determination to save Grant from his horrifying but inevitable fate.

Gunn never snickers at Starla’s efforts, nor does he offer Grant an easy way out. Slither holds up precisely because of this balance. Whether his characters are superheroes or space slugs, Gunn’s films are governed by that aforementioned “gooey sentimentality.” You connect deeply with those at the heart of the carnage, making it much easier to go along for the ride.

Slither is currently streaming on Amazon Prime.