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By Tom Foreman, CNN

The sun was shining on the Santa Cruz Mountains. The freeway from the San Francisco airport to San Jose was still buzzing in my ears when I stepped into the parking lot of an unassuming church and the most famous exorcist in America walked up.

“Hello, I’m Father Gary Thomas.” At 57 years old, he has an easy smile, an abiding love for the Giants and strong convictions about the nature of evil.

"You believe there is a devil?" I ask him as we settle in at a small, beautiful chapel near the church.

“Yes.”

“You believe that this devil acts upon people?”

“Correct.”

He says it with the certainty that I reserve for answers to questions like, “Did you bring your lunch?” but that’s no surprise. He has faced skeptics many times and never more than now, because his life and training as an exorcist in Rome are the inspiration behind the Hollywood film "The Rite."

Indeed, at the premiere, as the cameras swirled around the star, Anthony Hopkins, Thomas walked the red carpet alongside him. This movie, like salvation, is something the priest believes in.

“First of all,” he says, “it was very emotional for me. I found some of those scenes very riveting. I found some of them very profound. They’re very accurate. That’s what I’ve seen in real life.”

That’s saying something. "The Rite" is chock-full of heaving, cursing, ranting characters, who, according to the screenplay, are possessed by Satan, people who one moment seem fine and the next are raging against all that is holy.

And yet, Thomas says people who fear that very fate come to him constantly. “Well, often times they’ll begin the conversation with ‘Father, I need an exorcism.’ And my answer back to them is, ‘I don’t do them on demand.’”

But he does think a lot more of them need to be done. It is all part of a push by the Vatican to make more exorcists available to the faithful. Some in the Catholic Church believe the world is facing a rising tide of demonic activity, particularly in America, where millions are moving away from traditional faiths and looking for alternatives.

"A lot of folks dabble in the occult, or they will be involved in practices that … classical Christianity at least would consider to be idolatrous. People can get themselves involved in Wicca, or people will go see some sort of fortune-teller, or people will go to a séance, or they can go and they can learn how to channel spirits. …"

A vision of politician Christine O’Donnell fills my head and I interrupt. “But a lot of people would tell you up front, ‘I’m just playing around.’”

“Right. Absolutely. And it’s not,” he says, noting that those who feel adrift from the church and from others of faith are more likely to be drawn in. “Demons are always looking for human beings who have broken relationships.”

Simply put, Thomas believes just as surely as a person can summon God through prayer, through other rituals, the devil can be called, too.

Thomas says an exorcism usually takes from 45 minutes to two hours and involves reciting prayers, reading scriptures and using sacramental objects such as crucifixes and holy water. Of course, that’s like saying surgery involves a knife and some sponges.

It is vastly more complicated. Before the rite is even considered, there must be psychological testing by professionals, extended consultations and questions about drug and alcohol addiction.

Thomas says fully 80% of the people he meets claiming demonic possession have actually suffered some kind of abuse. An exorcism, he says, is the last step in a long process.

“I have a particular situation now,” he says, “where I think this particular person is suffering from a very unique psychological disorder, but she’s also been exposed to satanic cults, and I want to make sure that what we’re dealing with … is satanic or if it is psychological.”

Even when an exorcism is prescribed, it often must be repeated. Judging from Thomas' comments, it takes something of a trained eye to decide whether it is even working.

The movie, to be frank, complicates this whole discussion. Not "The Rite." Thomas says he likes that one, and found Anthony Hopkins a “delightful” man.

But rather the movie from 1973. "The Exorcist" captured America's imagination about demons taking over a person’s body and profoundly shaped the public's perceptions about the process of throwing those devils out. It was lurid, violent and unforgettable.

It was also based on a real exorcism in Washington, which was far less dramatic than the film. Thomas will tell you emphatically there are no spinning heads, spewing pea soup or levitating bodies.

But he has seen manifestations of possession. "Sometimes the person's head will begin to move in very rigid ways. Sometimes their eyes will roll. Sometimes there will be epileptic-like seizures," Thomas said. "Occasionally people will take on kind of a body language of a serpentine look, and they'll begin to stick their tongue out and use their tongue in ways that would look snake-like, and they'll coil up in a snake-like position."

“And these are things that you have seen in real life?” I ask.

"I have seen that," he said with a wry smile.

I’ve seen it, too. A few years ago I went to Tulsa, Oklahoma, to report on a Protestant exorcist who was holding a session in a hotel meeting room. Several dozen people filed in while, no kidding, "The Devil Inside" by INXS played on a stereo system.

Suffice to say, there were plenty of eye-rolling, seizure-like eruptions in the crowd as people cried out and the exorcist confronted them, pressing his Bible against their heads, and demanding that their demons reveal their names.

We talked to some of the participants before and after, talked to the exorcist, too. For all their heartfelt expressions of belief, I can’t help but ask Thomas the same thing I asked that night: Couldn’t all these folks just be acting?

"I don't think they're acting out in a conscious sense,” he says, “because many times … they don't remember the experience itself.”

What’s more, he says, occasionally the person will do something that defies explanation. "Sometimes the person will begin to speak in a language in which they have no competency in.”

Meaning, for example, someone who knows no German might start speaking precisely and accurately in that language. Thomas says he has witnessed that, too.

I stopped by the Pew Center in Washington, where some of the best research on religion is done, to ask about all this. Allison Pond is a charming young researcher who kindly sat me down before delivering some startling news: A Pew survey found more than one in 10 Americans have witnessed an exorcism, and when you narrow it down to Pentecostals it’s about one in three.

“Forty percent of Americans said they completely believe angels and demons are active in the world,” she told me, “with 28% telling us they mostly believe this."

That is the kind of information that needs more than a priestly explanation, so I roamed over to Georgetown University to talk to Ori Soltes, a theologian. The problem, he says, is that we can’t know for sure what people mean when they say they’ve seen an exorcism. Was it a formal ceremony? A personal revelation? A changed way of life?

Still, he has no doubt that claims of demonic meddling are high, because, after all, the year 2000 rolled around less than a dozen years ago, and at every millennium fears of the devil’s influence rise.

"My sense is that we are still in the backwash from the millennium,” he says, “but then you know ... events have helped to proliferate that: 9/11, the war in Iraq. And now as we approach 2012, suddenly everyone is very interested in the Mayan calendar and how we interpret the idea that the apocalypse is coming in December of 2012 at the time of equinox ... all that sort of stuff.”

So maybe it’s no wonder that Thomas is getting calls for exorcisms from not only Catholics, but also from followers of other faiths.

"How often?" I ask.

"I would say probably one out of 10."

Thomas says there are about 50 Catholic exorcists in the United States, and that’s not nearly enough. He’d like to see one exorcist in every parish. But until that day, he does not mind explaining over and over what exorcisms are really all about.

“It's a healing ministry. It's not hocus pocus. It's not smoke and mirrors. It's not magic. But I think if we don't respond to people who come in their very troubling moments, I think it diminishes us as a church."

Despite all that Hollywood has done to mythologize exorcisms, he still believes in the power of this rite, a power born not of fear, but of faith.

CNN's Eric Marrapodi and Katie Ross contributed to this report.