The actors in local haunted houses don't just want to frighten you, they want to scare you so badly that you'll lose bladder control. Really.Ghouls, ghosts, psychotic clowns and other performers can get a few extra bucks, and bragging rights, if they make paying customers wet their pants.

That particular "involuntary physiological response" is one of several that can occur when walking through one of the many local haunted houses, which draw huge throngs as Halloween approaches.

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The science of scaring • "When people get scared, they get adrenaline. They get that fight-or-flight response," said Julie Fox, an emergency-room physician at St. Mark's and Lone Peak hospitals.

To prove her point, the emergency-room physician electronically monitored KUTV-Ch. 2 features reporter Casey Scott at Nightmare on 13th, 320 W. 1300 South, Salt Lake City.

Before he entered, Scott's heart rate was 65 beats per minute; it spiked to 105 during his trip and was still as high as 99 several minutes after he exited — an indication of his high adrenaline levels, Fox said.

"Most people who go into it know it's not real. You want to be scared," Scott said after running the gantlet.

And according to Fox — and the heart monitor — our bodies don't distinguish between real danger and what's inside a haunted house.

"Fake things can be just as scary as real things," she said with a laugh, "because the part of your brain that controls that whole adrenaline, fight-or-flight response doesn't differentiate between something real and something imagined. The physiological changes that people have are exactly the same."

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The mad scientists • It's the same reason people are drawn to extreme sports like sky diving or hang gliding, which have a level of inherent danger.

That is what makes haunted houses exciting for people like Tim Riggs, whose love for haunting led to his career.

"During the daytime, I work for a defense contractor building military hardware," said Riggs, "and then in my free time I like animatronics."

He created a whole line of event automated control systems for Castle of Chaos, 120 W. 3300 South, South Salt Lake, and Nightmare Mansion, 5576 S. Redwood Road, Taylorsville.

Riggs became interested in haunted houses and electronics when he was in high school. That propelled him into engineering. He eventually earned an electrical-engineering degree from the University of Utah.

He has continued to work at various haunted houses during the past 10 years.

"I've got a long history doing Halloween events," he said. "I love it. It's fun. It's my hobby."

For Allegra Shurtliff, it's a full-time job.

"I take Christmas off, that's about it," said the production manager at Castle of Chaos. Shurtliff is in charge of continually updating and changing the venue. That's why she spends so much time inside the castle year round.

"It's why we're so pale," said Shurtliff, who does a little bit of everything at the venue. Including act.

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The actors who love to scare • At Nightmare on 13th, the 45-50 actors are paid; at Castle of Chaos, most of the 40-70 actors are volunteers.

"We do it because we love it," said Adam Christensen, who's been performing in haunted houses for 21 years. "I scare or make them laugh. Either way, they get their money's worth."

It can also mean a few extra dollars if he makes people pee their pants.

At Castle of Chaos, "it's called the wet sneaker award," said Shurtliff. "And, if it's confirmed, we actually will pay the actor for that scare."

How much they'll pay depends on how wet the sneaker gets.

"We've done as much as $20 in the past," Shurtliff said. "Then we started to go broke because it was happening a lot."

Nightmare on 13th offers something, too.

"Well, we don't track it," said Mike Henrie, one of the owners. "But it's really a good indication of a good actor. And we reward our good actors."

spierce@sltrib.com