Eroticism is in the eye of the beholder. In Japan, some women turn to electrically charged squid for sexual satisfaction. In the American world of masochism, one man begged to be tied on a spit and roasted over sizzling coals. His counterpart, a latex-loving dominatrix, reached ecstasy merely watching his pain.
What is abnormal may not necessarily be unnatural, according to sexologists who study the outer limits of the human psyche.
And, increasingly, as seen in a plethora of new books and films -- not to mention thousands of sites on the Internet -- kinky sex is getting more attention.
"To badly paraphrase Alfred Kinsey, [who pioneered sex research in the 1940s and 50s, filming couples in flagrante in his Indiana attic], 'the only unnatural sex act is the one you can't perform,'" said Robert Dunlap, a California sex therapist and filmmaker.
Paraphilias -- or socially unacceptable sexual practices -- are more common than most ordinary "vanilla" teleiophiles [those who desire adults] would imagine, according to Dr. Judy Kariansky, a sex therapist from Columbia University.
Though there is no hard data on what whether a spike in interest means a spike in actual activity, experts say anecdotally that couples are showing a marked interest in exploring new sexual intensity.
Dominatrix, Bondage, Flogging . . . Barbecue
In his 2001 film, "Beyond Vanilla," Dunlap interviewed more than 200 subjects who had one common denominator, some type of fetish -- bondage, flogging, knife play and fire, among others.
When asked "What is kinky?" academics, doctors, lawyers and even a congressman, shared fantasies like, "sex with a taxi driver in the back seat," "pouring candle wax on his testicles," "arresting someone and patting them down on the bar," "being gang-raped by many sets of twins, or better yet, triplets."
The film was widely praised and used by the University of Minnesota medical department at conferences on human sexuality and development.
Today, Dunlap is in negotiations for release of his latest film, a biography of the life of Xaviera Hollander, the madam who brought kinky sex out of the closet in 1971 with her book, "The Happy Hooker." His documentary earned early acclaim at numerous film festivals.
Also out this year are two books that appeal to those interested in sex outside the normal boundaries and that explore a world where pain, pleasure and often guilt intertwine.
One, "The Other Side of Desire," is a journalist's exploration of "the far realms of lusting and longing," including that reference to the pain aficionado who ordered her "servants" to barbecue her willing submissive.
Another, "The Adventurous Lover," which is part of the new "Joy of Sex" series, is a handbook for couples who want to experiment in a safe environment.
Kinky Sex on the Internet, Books, Movies
"It's a totally new revolution and it's really exploded," Dunlap told ABCNews.com. "The Internet has changed everything. So many people can go online and say, 'This is me. I love this. I am finding like types.'"
And for those who think this phenomenon might encourage anti-social behavior, he counters, "I don't think anyone was really damaged or hurt by book or movie."
Columbia's Kuriansky agrees that "what's weird, sick or kinky for you is what practitioners defend as 'normal' for them."
"Credit, or blame, the Internet, making information available in such a level playing field that outrageous acts have become so accessible they seem mainstream," she told ABCNews.com.
Throughout history kinky sex has emerged in myth, literature and in anthropology. Urban legends still persist that Catherine the Great had a special relationship with her horse.
Dunlap cites studies that in some African cultures, older women guide younger boys into their manhood and are "revered."
Couples Search for Sexual Intensity
But today, according to sex-perts, couples are looking for more intensity in sex lives, and interest in sado-masochism appears to be rising.
"After the pain threshold is crossed, they describe a type of ecstasy called 'flying," Dunlap found in his research. "It is no longer painful and gives an entirely sexual as well as psychological, transcendent place. Flying is bigger than any drug."
British relational therapist Susan Quilliam, whose revision of the 1972 classic, "Joy of Sex" sold 30,000 copies in three weeks when it was released this year in the U.S., confirms, "A lot is changing culturally."
"First of all, we live in a more sexualized society and there's the Internet," she told ABCNews.com. "Interest groups communicate with each other and reinforce their identity."
"It gives people permission and normalizes it and encourages them to explore the outer boundaries of their preferences," she said.
And now, her spin-off book, "The Adventurous Lover," is being billed as "perfect for the couple who want to push the boundaries: sections include fantasy, fetish, sex-clubs, foursomes and bondage."
Quilliam, who doles out advice on her "Sex in the City" radio show, has seen an increased interest in BDSM – or bondage, dominations, sado-masochism, as well as "swinging."
Creating a "safe" arena for experimentation is critical, she said, and couples should have special words, should they be uncomfortable, to call for "an immediate halt to the activity."
Dangers of Swinging: LoveAs for swinging, there's always the danger that one partner will fall in love someone other than their mate in a menage a trios.
She also warns, "Be careful, very careful if have a fantasy and you're putting it in to reality. It often disappoints."
"It has to be safe, sane and consensual," she said.
Universal Taboo: IncestTherapists say some universal tabooks, like incest, are even being challenged. Incest, was in the news in 2007, when a German brother and sister challenged the law so they could continue their relationship.
According to Hani Miletski, a Maryland sex therapist and author of the 2007 book, "Mother-Son Incest: The Unthinkable Broken Taboo Persists," a search for the words "mother son incest" yields nearly two million links on the Internet. Clearly an abusive behavior, she said it "breaks down the natural development of boys' sexuality."
Miletsky wrote another book -- "Understanding Bestiality and Zoophilia" -- after one of her patients admitted a "love affair" with his dog. She interviewed nearly 100 men who had indulged.
"People do it with all kinds of animals," she told ABCNews.com. "A lot of people are into dolphins and other sea animals."
"We also found a minority who prefer animals to humans," she said. "It's like a sexual orientation and they marry animals and treat like spouse whole love affair."
Such was the case with one man who had a relationship with his horse, according to Daniel Bergner, whose book, "The Other Side of Desire," just arrived in bookstores.
"I find I am closer to horses," the zoophile told Bergner, citing the "trust factor."
Guilt-Ridden Husband With Foot FetishBergner follows the journeys of four characters: a guilt-ridden husband with a foot fetish, a man infatuated with his step-daughter, a dominatrix who finds ecstasy in the pain of others and an advertising executive who is attracted only to amputees.
Bergner said he sees his characters as "metaphors for our own states of longing" and explores whether sexuality is defined by genetics, as many neuroscientists believe, or through "cultural scripts."
Studies by sexual anthropologist Gilbert Herdt of San Francisco State University reveal that in Papua New Guinea young boys are shepherded through their budding sexuality by engaging in ritualized homosexual oral sex with adolescents, ultimately embracing heterosexuality and siring children.
"Experience molds us," Bergner told ABCNews.com. "There's a sense that a charged experience, whether it is shame, or the opposite -- and pain can easily get mixed with pleasure -- leaves a sexual imprint."
Jacob, who was so ashamed of his foot fetish that he would not share the "monstrosity" with his wife, had struggled painfully through school. One psychiatrist suggested that the fetish began fear, as Jacob looked down, away from the teacher's gaze.
"That moment of terror got translated into an erotic sense of feet," Bergner said. "What we fear, we take control of."
Sympathy for SomeThough some of the sex acts witnessed -- including a sado-masochistic orgy led by a dominatrix known as the "Baroness" -- revolted Bergner, he said he felt sympathy for his characters, especially Ron, who creates ads with perfect models, and Laura, who lost both legs in a car accident.
"These two people have transformed each other's lives," he said. "Lust and love here are inseparable and redemptive."
Bergner and others who have interviewed those who cross boundaries most humans would regard as dark territory, say the compulsive power that compels them is part of the universal human story.
"No one wants to talk about Freud any more," he said. "One thing he knew that no scientist or psychologist displaces is that this drive is so central, so essential, and so powerful. The fact that we are living with that kind of powerful drive within in us is inherently threatening."
"Part of me thinks people are more receptive and comfortable taking risks sexually," said Bergner. "But part of me thinks we are pretty much afraid -- afraid because the force of the erotic is pretty strong and probably anarchic, and therefore, maybe we worry that if we step a little over the boundaries, we might not be able to step back."