The designers behind amusement parks' most popular attractions roller coasters and haunted house--are master manipulators of our deepest fears.

In Orlando, Florida, David Clevinger stands in a back corridor of Terror on Church Street and listens expectantly as customers make their way through the haunted house's passages. Suddenly screams erupt, sending Clevinger, the attraction's artistic director and operations manager, into gales of glee. "I love that sound," he chortles. So does Dave Focke. Watching shrieking riders hurtle through the drops of The Beast, the massive wooden coaster at Paramount's Kings Island near Cincinnati, Ohio, Focke beams with pride. "Guests come off breathless, hearts pounding, scared out of their wits," exults Focke, the park's vice president of construction and maintenance. "And wanting to get in line to go again!"

Call them shock meisters, terror tacticians, spookologists and boo-ologists. The small band of designers who create the roller coasters and haunted houses that are amusement parks' premier attractions are master manipulators of our deepest fears. They get us to walk through pitch black hallways and step into cutaway coaster cars that dangle our arms and legs. They exploit our most closely held vulnerabilities--and make us like it.

For designers, primarily engineers for coasters and theatrical artists for haunted houses, turning fear into fun depends on illusion. No matter how precarious a roller coaster or alarming a haunted house may appear, it must be totally safe. "We always try to make them look and feel more dangerous than they really are," says Michael Boodley, president of Great Coasters International, Inc. of Santa Cruz, California.

Though the experience offered by roller coasters and haunted houses diverges dramatically--it's the difference between pushing a wagon over a steep hill versus telling campfire ghost stories--the attractions are constructed of common elements. Both draw on all our senses, both rely on surprise for their shocks and both quote heavily from the movies (coasters replicate action-adventure perils, a la Indiana Jones and Star Wars, and haunted houses feature quasi-Frankensteins and Friday the 13th Jasons).

But the biggest common denominator is that the two feed on the same basic fear: loss of control. Once a coaster takes off, passengers can do nothing but sit or, on some rides stand, and scream. "The closest thing to compare it to is driving with an idiot," observes Boodley. Lynton Harris, director of Madison Scare Garden, an annual fright fest in New York City, also uses an auto analogy for haunted houses. "It's a hundred degrees outside, and you'd expect to get in a car and have air conditioning, and all of a sudden the heater gets turned on," he says. "Then the doors lock. Cocky as you are, you realize you're not in charge."

With roller coasters, the psychological games start before customers even get into the train. Boodley purposely makes his wooden coasters as diabolical looking as possible. "It's kind of like a black widow spider web," he explains. "It's a very, very pretty thing, but when the black widow gets you..." Queueing customers at Outer Limits: Flights of Fear, one of 12 coasters at Kings Island, are treated to dim lights, alien noises and a video of a space station in the grip of a mysterious force. "Even after having ridden that ride probably close to a hundred times, I sit there anticipating the start, and my palms still sweat," says Outer Limits designer Jim Seay, president of Premier Rides of Millersville, Maryland.

Whether the traditional chain-driven wooden or steel clackers or the newer linear induction motor (LIM) rides that harness electromagnetic force to blast off trains, all roller coasters play on two related--and universal--terrors: fear of heights and fear of falling. "The loops and elements, they come and go, but the coaster always has to have the big drop," says Focke of Kings Island.

Traditional coasters provide an excruciatingly slow buildup to the plunge. "There's a lot of self-abuse on that chain lift," says Boodley "Your own mind puts you in a state of paralysis." (Wooden coasters also creak, rumble and clickity-clack naturally as they flex, but riders get a queasy feeling that the structure is about to collapse. "That's probably one of the funniest things we as designers get to appreciate," says Boodley.) LIMs, on the other hand, rocket you into terror with trains that go from 0 to 60 mph in under four seconds. The big drops are actually shorter on LIMs, but the sense of speed sets hearts pounding.

Most coasters travel below 70 miles an hour, slower than many people drive, but designers heighten the sense of speed and danger with close flybys of terrain, buildings, people, even other trains. At Busch Gardens Tampa Bay, Montu dives riders into five trenches, one of which emerges through the patio of an ersatz Egyptian temple. "Not knowing exactly where the bottom is or where you come out is important," says Mark Rose, the park's vice president of design and engineering. "If you could see the whole thing, then you could kind of play it out in your mind." Some coasters, like Outer Limits and Disney World's Space Mountain, intensify the fear and suspense by keeping passengers in the dark for the entire ride.

Upping the vulnerability quotient even further is a recent innovation: inverted coasters which suspend riders below the track and carve away as much of the train as possible. "There is less fiberglass, less coach around you, so your feet are just hanging out there," notes Rose. During one stretch of track on Montu, passengers' soles skim just 24 inches above the ground. Riders also get dangled over a pit of live Nile crocodiles.

A coaster's effects, though, are not all illusory. Passengers pull close to 4 positive G's on some plummets. They turn upside down on loops and rotate head over heels through corkscrews. They literally feel the wind in their hair and, on a LIM coaster launch, the air in their eyes. Human bodies don't commonly experience such acrobatic maneuvers, and that in itself is psychologically disorienting. "Anytime you put a rider in a situation they're not used to, there's an element of the unknown," declares Boodley. "And for 80% of people, fear is the unknown."

The biggest unknown of all is death, and creators of haunted houses are masters at exploiting our fear of dying, especially in a gruesome manner. To unnerve guests, designers depend on two elements. The first is setting a spooky mood with sights, sounds, smells and "feels"-- "all the things that make you uneasy," says Drew Edward Hunter, co-chairman of the International Association of Haunted Attractions and design director of haunted attractions at Sally Corporation of Jacksonville, Florida. "Then you have the second part, the attack, the out-and-out scare. I don't think you can have one without the other."

For the "creep-out" effect, haunts are always dark; skeletons, skulls, fog, ticking clocks and screaming ghouls abound. "On my sets, I try to capture a claustrophobic feeling," says Terror on Church Street's Clevinger. "I bring my ceilings low, the walls close." To further emphasize the sense of enclosure, he hangs tree branches, Spanish moss, rags and spider webs.

Just the suggestion of something loathsome will give customers the screaming meemies. "Do the sounds of insects, and people scratch their heads all the way through," says John Denley, president and owner of Boneyard Productions of Salem, Massachusetts. Run a soundtrack that whispers of rats, turn on ankle-aimed air hoses and professional football players tap dance. A strong whiff of formaldehyde and you have the scent of death, "no matter what country you're in," says Clevinger.

The second part of the equation is the scare, which, say spookologists, is really a "startle." "All scares are primarily based on two things," instructs Edward Marks, president of Jets Productions of Chatsworth, California. "One, it's there and does something you don't expect it to do, or two, it's not there and it appears."

In Terror on Church Street, customers come upon Hannibal Lecter, the cannibal psychiatrist of Silence of the Lambs. He yells and lunges against his cell's bars, drawing yelps from viewers. The cries quickly subside into nervous tittering. As guests make their way around the bars, Lecter follows along inside. Then, just when viewers feel safest, Lecter opens the cage door and steps out. "The guys who were taunting him usually scream the loudest," observes Clevinger.

In the second type of gag, designers have people or objects suddenly emerge from in front, beside, above or below patrons. A surefire gag--and the simplest of all--is dropping a spider on a person's head. "We call that a $2 scare," says Harris of Madison Scare Garden. "It's the best value-for-money scare we've ever used."