What is it about science-fiction and horror movies that unleashes the cinematic cheese? From hilarious atomic monsters to UFOs dangling from strings, the history of genre films is riddled with patently absurd imagery. With Piranha 3D chewing its way into theaters Friday, the flesh-ripping–fish franchise — which got its start in the '70s at the hands of schlock-shock producer Roger Corman — aims for a bloodletting upgrade by showcasing the carnage in three-dimensional splendor. Director Alexander Aja's modern-day reboot brings to mind a welter of predecessors that made melodramatic mincemeat from mutant DNA, flimsy rocket science, stiff acting and hilariously un-special "special effects." To assemble this round-up of sci-fi's cheesiest hits, Wired.com recruited Pyschotronic Film Society founder Mike Flores, a specialist in B movies. Also weighing in are the movie-mocking madmen from Mystery Science Theater 3000 spinoff RiffTrax. (For more cinematic high-larity, RiffTrax's Mike Nelson and company are staging RiffTrax Live: Reefer Madness, which will be broadcast live by satellite to 500 theaters at 8 p.m. Eastern Thursday, tape-delayed at 8 p.m. Pacific.) Above: Piranha After Roger Corman saw Jaws smash box-office records in 1975, he produced the original Piranha, his own cheapo aquatic horror story. Keep reading for a run-down of sci-flicks so bad they're good. Or something.

The Creeping Terror RiffTrax member Mike Nelson describes 1964's The Creeping Terror as "a very, very cheap movie. The director couldn't afford the traditional 'dialogue' seen in many other movies, so he just shot it without dialogue and added narration in post-production. The creature? A carpet sample. I'm not kidding. It's a large section of carpet, probably pulled out of a dumpster behind a bowling alley."

Killer Shrews Mike Nelson recaps the perverse appeal of this 1963 mutant epic: "The guy who played Sheriff Rosco P. Coltrane is stranded on an island with a boring scientist and his hot daughter. It sounds like the setup to a joke, and it pretty much is, as they are soon attacked by the 'shrews,' which are really just badly behaved dogs draped in bathroom rugs and wearing bad Halloween masks."

Troll 2 The sequel to Troll is "pretty great, because there are no trolls in the movie, only goblins," says Mike Nelson of RiffTrax. "And they look like pieces of chewed gum rolled in coffee grounds and hair. The biggest 'reveal' in the film is that the town infested with goblins is called 'Nilbog.' It takes a good long time for our heroes to puzzle out the fact that 'Nilbog' is 'goblin' spelled backwards!"

The Giant Spider Invasion RiffTrax member Bill Corbett, who skewered The Giant Spider Invasion on Mystery Science Theater 3000, remembers the flick as potentially dangerous. "Aside from the silly premise that a meteor could cause some sort of interdimensional gateway, which leads (somehow) to an army of Brobdingnagian spiders — well, by the end of the movie the giant spider is obviously a car with a spider float glued onto it. Scary! But only in that you might laugh until you choke."

The Horror of Party Beach Bill Corbett mocks this 1964 flick, "which blames our old friend toxic waste for the creation of lumbering half-human, half-fish monsters. Slow-moving, dopey-looking and easily killed with a handful of sodium (yep, sodium), they are poor excuses for horror. Luckily the jaunty beach music of scrawny trio The Del-Aires saved this movie from being a total snooze."

The Happening Bill Corbett ripped this 2008 movie for RiffTrax. "I wondered if director M. Night Shyamalan might be involved in one of the slowest, slyest hoaxes of all time: What if a once-reasonably respected auteur just kept producing more and more ridiculous work?" Corbett asked. "But no. There is no meta-joke here, just the sad joke of this movie's premise: The monster is the wind. Yes. The wind. I have nothing more to add."

Robot Monster "I'm particularly fond of creatures meant to strike terror into our very souls, but who instead fill our hearts with laughter and love," says Kevin Murphy of RiffTrax. "To wit: Ro-Man from Robot Monster. Suspiciously hairy, no doubt matted, probably redolent of dead bear, Ro-Man summons lightning and oversized terrarium lizards at will. Those are his powers. His liabilities? Watch how he lopes along like Shaggy in Scooby-Doo. He's got a boner for the female lead. He has issues working his ham radio. By the end you just want to hug the big guy, minus the smell and the boner of course."

The Amazing Colossal Man For this 1957 black-and-white picture, Kevin Murphy singles out Glen Manning for ridicule. "I'll be brief: A giant, be-diapered baby throws a tantrum and destroys most of Las Vegas. Why this is not already a Happy Madison remake starring Rob Schneider is one of life's most puzzling mysteries."

Cloverfield Kevin Murphy has his own pet name for the monster in 2008 monster movie Cloverfield. "I call him Clovie cause it just fits, like Toxie from Toxic Avenger," Murphy says. "He might be the lamest CG monster not to appear on a sci-fi movie, but keep in mind he's systematically killing every douchebag in Manhattan. This is why I love him so."

The Brain That Wouldn't Die B-movie expert Michael Flores likes the fact that the antihero of this 1962 flick haunts strip clubs to find body parts as transplants for his dead-but-still-yapping wife. "Science marches on!" Flores says. "The wife is a decapitated head nagging you from the tray on the table her head rests on. Even after decapitation, she is going to get the last word!"

Barbarella French director Roger Vadim cast his girlfriend Jane Fonda as a nubile "astronavigatrix" dispatched by Earth to track down a "positronic ray weapon" in 1968's Barbarella. "Wonder what a striptease would be like in a weightless situation?" Michael Flores muses. "Jane Fonda moved science forward by showing us in the opening credits. Kind of brings a tear to your eye, don't it? "The film's plot has everything but the kitchen sink and still doesn't connect. Barbarella is a glorious car wreck of a movie. The film managed to waste the talents of mime Marcel Marceau — not even Terry Southern and seven writers could save it. Without Jane Fonda, sexually confident beyond her years, it would be among the most awful failed films of all time."

Piranha 3D The film's flavor comes across in actress Jessica Szohr's account of her on-set Piranha 3D experiences. "There were times when fish were grabbing me, and so they put people with green gloves on underneath the water and had them grab at my ankles," she told New York Magazine. "They were actually really grabbing me." As for the action sequences, Szohr recalls, "There's a scene where I'm in a boat that's sinking, and I have to fight these piranhas off with a frying pan. A couple of stunt guys shot water guns at me so I knew where to aim with the pan."

Galaxy of Terror Galaxy of Terror's descriptor — "Hell has been relocated," courtesy of schlockmeister Roger Corman — ranks as one of the better B-movie tag lines of all time. The movie, also known as Planet of Horrors and the more scholarly sounding MindWarp: An Infinity of Terror, gives production-design credit to Avatar director James Cameron for his low-budget spaceship effects. Robert Englund makes a pre–Freddy Kreuger appearance. The plot? On a planet, named Morgenthau for no discernible reason, astronauts tries to find crew members from the missing starship Remus.

Battlefield Earth Expensive to make but cheap to look at, this intergalactic showdown represented a labor of love for star-producer-Scientologist John Travolta. (Church of Scientology founder L. Ron Hubbard wrote science fiction when he wasn't inventing religions.) Universally reviled by critics — rating just 9 out of 100 on Metacritic — the turgid drama is based on Hubbard's 1982 novel about a hero named Jonnie Goodboy Tyler. Enough said.

The Beast of Yucca Flats A Soviet scientist defects, flees into the Yucca Flat desert and turns into a "beast" because of radiation poisoning in this 1961 movie. The kicker: All dialogue was dubbed in later either as voiceover or with characters facing away from the camera so you can't see their mouths. Beast of Yucca Flats writer-director-narrator Coleman Francis, doubtless "inspired" by 1960's Psycho, added his own nude shower-murder scene at the start of the film. The tawdry crime goes unmentioned for the rest of the movie.

The Avengers This disappointing 1998 superhero picture brought out the worst in talented actors including Uma Thurman, Ralph Fiennes and Sean Connery. Cheap-looking special effects, flimsy plot and ludicrous story lines added up to a movie that wasn't even bad enough to be good.

Slither Serving up post-modern cheese for moviegoers who were in on the joke, Slither director James Gunn in 2006 paid tongue-in-cheek homage to Invasion of the Body Snatchers, Tremors, Night of the Living Dead and Night of the Creeps with his story about a South Carolina businessman infected by alien toxins. The virus eventually turns the townspeople into pet-eating zombies.

Plan 9 From Outer Space Ed Wood directed this sci-fi invasion flick on a literal shoestring when he dangled flying saucers from pieces of thread clearly visible on screen. When Bela Lugosi died in 1956 during the shoot, Wood hired a chiropractor friend to replace Lugosi and hid his face behind a cape. Tim Burton and Johnny Depp revisited the DIY filmmaker's life and times in their affectionate 1994 biopic, Ed Wood.

Sins of the Fleshapoids Bronx twins George and Mike Kuchar set Sins of the Fleshapoids a million years in the future, when mankind has thoroughly debauched itself in the pursuit of sex. Robot slaves do all the work until they finally figure out how to mate, giving rise to a new race of "fleshapoids." It's hard to tell from the stiff acting which characters are robots and which are supposed to be human, with George Kuchar contributing a supporting performance. In their earlier movie, Night of the Bomb, brother Mike can be spotted on camera when he substitutes his own buttocks as a stand-in for his lead actress, who refused to take part in the scene.

Tremors Run for your lives, they're giant burrowing ... gophers? Actually, this 1990 mutant flick sends Kevin Bacon and his cast mates into freak-out mode once they find out about tentacled creatures called "graboids." The 30-foot-long creatures like to snag prey from underneath, so you never know where they're going to strike next. Think of it as Jaws in the desert. With giant worms.

Clash of the Titans This 2010 remake was hard to take seriously. Fake-looking giant crabs and sea monsters consistently played second fiddle to the actors' wooden performances, complete with ancient marketplace crowd scenes that unintentionally call to mind Monty Python's Holy Grail lampoon. On the plus side, the film gave Liam Neeson, playing Zeus, the best catch phrase of the season: "Release the Kraken!"

Attack of the Puppet People Not to be confused with two dozen other "Attack of" projects, this goofy 1958 thriller tried to ride the coattails of The Incredible Shrinking Man by portraying a demented scientist who uses a ray-gun device to shrink women. In his lair, they try to live life as doll-size slaves. As the Attack of the Puppet People trailer says, "The loss of love has turned this mild-mannered man into a maniac who wants to make you his plaything!"

The Aztec Mummy vs. the Human Robot Sci-fi meets Mexican mythology in this low-budget 1957 saga. First, the evil Dr. Krupp hypnotizes a beautiful woman into snatching ancient jewels guarded for centuries by an evil Aztec mummy. Then he gets down to business and invents a robot. The final confrontation takes place in a cemetery between the mummy and Krupp’s metallic man.

The Monster's Ship An example of Mexico's midcentury sci-fi boom, 1959's La Nave de los Monstruos, aka The Monster's Ship, follows two Venusian women who crash-land in Chihuahua, Mexico. From there, Beta and Gamma enslave handsome earthlings with their bloodsucking skills.

Slave Girls From Beyond Infinity This 1987 outer-space action flick represents an example of what Portable Grindhouse author Jacque Boyreau affectionately calls “super trash.” The plot of Slave Girls From Beyond Infinity bears a remarkable resemblance to this summer's Predators: Astronauts Daria and Tisa crash-land on a planet's jungle preserve, where Zev hunts them for sport as part of "the most dangerous game."