It was late in the afternoon, while leading his last daily tour of the historic Mark Twain House, that Jason Scappaticci glimpsed something that would change his thinking about the paranormal.
Assuming it was a visitor who had separated from the group, he walked over. But instead of finding a stray guest, he says he found a supernatural one – a transparent figure of a woman dressed in a hoop skirt floating down the hallway.
"It was definitely a ghost," Scappaticci said. "I just stopped in my tracks and froze for a second and stared at it."
For four years, Scappaticci, 28, has worked at the Hartford, Conn., home of the famed American author Samuel Clemens. He had heard other tour guides whisper about voices they'd heard in the hallways, but said he was a skeptic until he had his own experience a few years ago.
Since then, other guides, visitors and security guards have come forward to tell their own stories of unexplained encounters in the 19th century Victorian mansion.
Some hear voices, others laughter. Some see apparitions of women, others visions of young girls. All swear spirits of the Clemens family haunt the house.
Though many dismiss such claims, a growing group of people around the country is embracing them – so-called paranormal investigators who, in many cases, employ souped-up technology and science-inspired methodology to search for evidence of the supernatural in historic sites like the Mark Twain House to seemingly ordinary homes and every place in between.
Jason Hawes, 37, and Grant Wilson, 35, stars of cable channel Syfy's "Ghost Hunters," estimate that there are thousands of paranormal investigators around the world.
The Rhode Island-based Atlantic Paranormal Society, which Hawes founded in 1990, now has a group in every U.S. state and 12 other countries around the world. The pair acknowledges that their show and others like it have given the ghost hunting community a boost in numbers and profile.
"There are a lot of people out there who believe that they're having problems and need someone," Hawes said.
Though they don't like to discuss the details, both men say they've had personal paranormal experiences that push them to help others.
"It's good that they know that people like us are out there. We do this for free," Hawes said. "We want to empower them and give them their homes back and their strength back and their lives back."
With a puckish nod to his pop culture predecessors like "Ghostbusters," he added, "Who else are they going to call?"
But though they hunt for the supernatural, they say they retain a healthy dose of disbelief.
"We are skeptics, otherwise we would believe everything," said Wilson.
The most interesting cases make it onto the show, but Hawes said they're able to debunk 80 percent of the claims of the paranormal.
After interviews with their clients, the investigators reach into their trove of ghost hunting technology.
Electromagnetic field meters detect spikes in electromagnetism that could cause some people to hallucinate and imagine spirits that aren't really there. Digital infrared cameras capture images that are invisible to people.
Surveillance cameras record 360 degree panoramas of rooms thought to be inhabited by ghosts.
As they painstakingly pore over the data, the team separates fantasy from reality to offer clients some kind of explanation.
"You have to take shreds of science and technology and put them to work for you and see what works," said Wilson.
Often they learn that a flickering light isn't a ghost but a bad switch or a room isn't haunted but contains hallucination-inducing unshielded wires. Other times, they have no explanation.
"There's a lot of weird things out there that we can't explain," said Hawes. In one investigation, they observed a 9-year-old girl, seemingly possessed, with the strength to lift objects too heavy for most adults. In another, they encountered a person pushed up a flight of stairs ostensibly by an invisible force.
But even when they find mundane explanations for extraordinary claims, they say they gain something.
"Every case is a learning experience. We're happy if we find something or not. We learn something for future cases," said Wilson.
And patience, it turns out, is it a critical trait for aspiring paranormal investigators. Though tracking ghosts and spirits sounds glamorous, devoted hunters acknowledge that the work can be tedious.
"It's really boring," said Cheri Esperon, 38, founder of the Northern Alliance of Paranormal Investigators in Kenosha, Wisc.
Some investigations involve listening to recorded white noise or sitting in an empty building for hours on end, waiting for something out-of-the-ordinary to appear.
"For a lot of people, the reward is late in coming," she said.
But Esperon, who is an office manager for a local church, said that what led her to start the group -- and what keeps her hooked -- is "morbid, rabid curiosity."
She said she'd been chasing urban legends for years but, after seeing Syfy's "Ghost Hunters," decided to come out of the "paranormal closet." She now works with about a dozen other investigators on roughly two cases a month.
They end up debunking about 65 percent of their claims, she said, but the remainder is enough to drive them forward.
"I don't have the answers yet, every answer I get gives me another question so I keep going," Esperon said.
Though these investigators say they employ the scientific method and critical thinking in their craft, seasoned skeptics say the results speak for themselves.
"You have literally hundreds of groups in North America that have done tens of thousands of investigations and yet none of them are finding anything definitive," said Benjamin Radford, managing editor of the Skeptical Inquirer Magazine.
Radford said he doesn't dismiss ghost hunters and has even investigated reported hauntings himself, but he said, "If you're going to do it, do it right."
Sound science requires sticking to a process based on gathering empirical, measurable evidence, not picking and choosing the pieces that most support your case, he said.
In one case he investigated in a Santa Fe, N.M., court house, a deputy saw a mysterious white glowing figure on surveillance camera footage.
The mysterious figure made headlines as locals circulated stories about resurrected Native American spirits from a nearby cemetery.
But after four days of haunting the court house himself, Radford discovered through trial and error that the "ghost" was actually an insect caught on camera in the morning sunlight.
"There are a lot of things that humans can't explain but that doesn't mean that they're supernatural," he said. "Something I can't explain doesn't necessarily equal ghost."
Sometimes it's simply more work and investigation that separates the explained from the unexplained, he added.
"It's not that things that are explainable are of a different category, it's just something someone has put more time and research into it," he said.
And ghosts, Radford pointed out, are far more deep-seeded that other kinds of paranormal phenomena.
"Ghosts are wrapped up in a religious world view," he said. "Virtually every culture has a belief in ghosts."
Though the ghosts of movies and television shows are often frightening goblins or chilling demons, Radford said that for many ghosts are dead loved ones or spirit guides. As long as people believe in an after-life, there's room for a belief in ghosts.
So what of the reports of ghosts haunting the house of Mark Twain, who himself was thought to be interested in the spiritual movement and the stuff of séances? What of claims that Twain's daughter Susy, who died in the house at age 24, continues to roam the halls?
In September, Hawes and Wilson traveled to the historic home to investigate the reports from Scappaticci, other staff and visitors. They unloaded their technology and spent about a week trying to explore the claims.
And what did they find?
Well... they couldn't quite say.
Though they may be able to stretch the laws of reality, they're still beholden to the laws of reality television.
Hawes said their findings won't be revealed until the episode airs later in the season. But, he teased, "there's just a lot of great stuff coming out... People will be really happy."