This is not a horror movie. It is a real-life mass at Acuna's evangelical exorcism school -- thought to be one of the first in Latin America.
The bespectacled 54-year-old Lutheran pastor trains lay people as "exorcism consultants".
"They study the devil's character and how he works," he told AFP, amid the rich smell of incense.
"The exorcism consultant will be able to determine where there is a case of a demonic presence, possession, oppression, obsession or a curse."
Acuna has a passionate following. Crowds of hundreds flock to his Good Shepherd church on exorcism nights.
He has also earned the suspicion of fellow clergymen.
His 35 students pay $47 a month for his three-year, part-time course in "Parapsychology, Angelology and Demonology."
He insists it isn't about the money.
"The mystery of the unseen provokes fascination in some people, but also a lot of criticism," he said.
"I have been called all kinds of names. But I didn't choose to be an exorcist. It is a calling from God."
- Human desire -
Photographs on a wall show Acuna meeting celebrities and even Pope Francis, a fellow Argentine.
But unlike Francis and most other Latin Americans, Acuna himself is not Catholic.
He is a protestant bishop from the New York-based Association of Independent Evangelical Lutheran Churches.
Clergy at four other Lutheran churches contacted by AFP distanced themselves from Acuna and his school.
"We have to ask ourselves how much of what is being advertised is true, and how much is business?" said one of them, pastor Esteban Tronovsky, who believes exorcism cannot be taught.
"How much of it is about winning fame, prestige, power and money? And how much of all that is actually linked to God's truth?"
- Spitting blood -
In 2001, a teenage girl started writhing and speaking in tongues during a mass.
"On that day, with my first exorcism, I introduced myself to the devil," he says.
"Being an exorcist became my way of life."
Acuna's monthly public exorcism sessions at his church in a suburb of Buenos Aires are noisy, passionate affairs.
At one such gathering attended by AFP, participants swooned and yelled as demons appeared to possess them.
One woman spat out a red liquid. Acuna told AFP it was because she had "made a pact (with the devil), sealed with animal blood."
- Blessing -
Acuna's students include housewives, lawyers, a writer and an architect.
One of them, Gloria Sanchez, 60, said she used to live in a haunted house.
Now she wants to learn "to help other people overcome, understand and resolve such situations," she says.
"This course is giving me explanations to many experiences in my life that no one could explain," she said.
"I feel blessed with power, to be doing this course at my age."
At one of Acuna's training sessions, IT technician student Eduardo Klinec, 53, practiced what he has learned.
He demonstrated how to light a candle for use in an exorcism.
"With knowledge," he said, "your fear and skepticism disappear."
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