Something snapped in the screaming room in the late 1970s.

Suddenly, the lurking boogeyman changed his stalking strategy and prime target. The new breed of killer – Michael Myers in “Halloween,” Freddy Krueger and Jason Voorhees in the original “Nightmare on Elm Street” and “Friday the 13th” – attacked more frequently and seemingly without provocation. And, most curious, he (it?) preyed almost exclusively on sexually active teenagers.

Was it the new, punk-oriented youth audience, which naturally gravitated to weirdos? Was it the new, looser definition of what constituted an “R” or restricted rating? Was it the more sophisticated makeup effects, taken to a new level in 1978 by “Dawn of the Dead” and its ilk? Or was it the filmmakers themselves, who, battling studio blockbusters like “Jaws” and “Star Wars,” were seeking cheap, straight-for-the-jugular alternatives?

With the arrival Friday of New Line Cinema’s “Freddy vs. Jason,” that inevitable fusion of “A Nightmare on Elm Street” (1984) and “Friday the 13th” (1980), we decided to check in with a few experts in the field, including John Carpenter (director of the original “Halloween”), Sean S. Cunningham (director of the first “Friday” and producer of the latest installment), and actors Robert Englund and Ken Kirzinger, who are squaring off as the quip-y, fire-scarred Freddy and the hulking, unstoppable Jason.

Besides New Line’s $35 million sequel – hyped as a brains-vs.-brawn matchup – the other upcoming slasher attractions are “Jeepers Creepers 2,” “Cabin Fever” and a remake of “The Texas Chainsaw Massacre,” still for many the ne plus ultra of fright.

“It’s no coincidence that these movies started after Vietnam, Watergate, Nixon’s resignation the Iran hostage crisis,” recalls Carpenter, who, since unleashing his masked killer in “Halloween,” has turned more toward science fiction. “There was a lot of disillusionment out there; it was an unsettled time, and young people were hungering for entertainment. Horror managed to sneak its way in. Who would have thought the cycle would last this long?”

After playing dream-stalker Freddy in all eight “Nightmares,” as well as on “The Simpsons,” Englund has the equivalent of a Ph.D. in horror. (He stresses that what he does is “more Kafka-esque than slasher-esque.”) And at 54, he’s old enough to remember the start of the slasher craze. He traces the trend to “the nihilistic punk sensibility.”

“Back then, there wasn’t the kind of right-wing, born-again viewpoint we have now,” Englund says. “Instead, there was a sort of garage band, cheap thrills sensibility.”

Suburban teenagers were ripe to lose their innocence at the hands of Freddy and Jason, Englund continues. He points out that Wes Craven, who directed the first and seventh “Nightmare,” has called Freddy “the bastard father of us all.” “I’m not sure what that means,” Englund laughs, “but I think it has something to do with the sins of the father, the sins of another generation, being passed down.”

Cunningham waves off much of this. For him, the “Friday” movies were always potboilers meant to put food on the table. The original “Friday” cost $500,000 and grossed almost $100 million worldwide. “There were no expectations back then,” says the producer. “They were low budget, no star, almost no story. All we had was a scary title. The idea was to make the most no-frills movie we could make and still create something that was scary-fun, that played on every teenager’s primal fears.”

Canadian stuntman-actor Kirzinger, 43, inherited the Jason hockey mask from Kane Hodder (“Friday VII-X”) after serving as stunt coordinator on “Friday VIII.” For Kirzinger, the slasher craze always has been synonymous with escalating violence. “These movies pushed the limits on violence and took viewers to a new level of gore,” he says from his home in Vancouver. “It’s like watching an accident unfold. There’s always this morbid curiosity: You want to see a bigger, gorier accident.”

And the filmmakers’ response? “OK,” Kirzinger surmises, “how gruesome can we make this killing look?”

Our panel also points to the Motion Picture Association of America’s rating system that, in the “70s, allowed a new level of R-rated carnage. “Censorship was at a low ebb,” says Englund. “Before, there were rules and we had to tread lightly through certain areas,” recalls Carpenter. “With the new freedom we pushed the violence and sex as never before.”

Bottom line? These movies are cheap and lucrative, especially now that fans watch them again and again on video and DVD. “Believe me, the movie business just goes where the money is,” says Carpenter, who was approached years ago about a “Jason vs. Michael Myers” matchup. Because of contractual hassles, it didn’t happen, but Carpenter still holds out hope for the card, especially if “Freddy vs. Jason” performs.

Milking the dog days of summer, New Line has spent a bundle advertising “Freddy vs. Jason” and will open it on more than 2,800 screens. And like all good heavyweights on the eve of combat, Englund and Kirzinger are doing their bit, trash-talking one another.

“Jason is bigger, meaner, this generation’s Frankenstein,” brags Kirzinger. “He symbolizes the inevitability of death. Nothing can stop him.”

“Jason definitely has the reach on me, but he’s a big dumb dog!” counters Englund. “As long as he’s in my world, the dream world, I can beat the crud out of him.”

“Jason is definitely favored,” acknowledges Cunningham. “But it’s all just silliness.”