Around his seventh birthday, the boy said, his father called him over to the family computer and told him to watch the video playing on the screen. There were naked women, the boy said, and naked men. They were having sex.

The boy, testifying Thursday in Luzerne County Court, said his introduction to pornography evolved into thrice weekly viewings with his father, designed to familiarize him with sexual intercourse. On his eighth birthday, the boy said, his father led him to an upstairs bedroom at their Plymouth home and demanded he have sexual intercourse with his mother.

"He called me over to have sex with my mom," the boy, now 14, said at the trial of his parents, Robert Caravella and Carol Hann, for sexual abuse and endangering the welfare of a child. "He had been building me up to it."

The boy, homeschooled through an online charter school and shielded from society for most of his life, said he did not realize the encounters with his mother were wrong or criminal until four years later, when a shocked foster parent told him she would not require him to have intercourse.

Caravella and Hann, testifying Thursday afternoon, denied showing the boy pornography or forcing him to have sex with her. They also denied charges that the boy lived in squalid conditions or that they neglected the boy's health and hygiene.

Caravella, 53, is charged with conspiracy to commit rape of a child, corruption of minors, endangering the welfare of children and distributing explicit sexual material to minors.

A jury convicted him in April on 13 charges for sexually abusing two underage girls between 2002 and 2005. A judge has postponed sentencing in that case until after the conclusion of the current trial.

Hann, 45, is charged with rape of a child, corruption of minors, endangering the welfare of children and incest.

Closing arguments are scheduled for this morning. Jurors could begin deliberating the charges by noon.

Caravella, in his testimony Thursday, called the pornography allegation was a "lie," and the idea that his son had sex with his wife, "impossible."

"I believe my wife when she says it never happened," he said. "And if it never happened, how could I know anything about it?"

Hann described herself as a "good Christian woman" and blamed a "bunch of backstabbers" in her family for compelling the boy to make false allegations against her and her husband. She said her size - 5 feet 10 inches and, at the time, well more than 300 pounds - and a tailbone injury from a 2007 car accident made it impossible for her to have sexual intercourse.

The boy, speaking in more graphic terms than the victims who testified at the June trial of former Penn State defensive coordinator Jerry Sandusky, painted his parents as monsters.

After his eighth birthday, the boy said, he and his mother fell into a routine of sex as much as four times a week.

Each time, he said, "she'd start by taking her clothes off and I'd follow."

At one point, gauging the boy's understanding of the activity, Assistant District Attorney Jenny Roberts asked the boy to define what he was doing.

"Intercourse," the boy said. "It's when a man's genitals go into a woman's genitals."

Later, during their pornography sessions, the boy said, the squat, mustached Caravella would coach the boy on his performance, the boy said. Caravella would use the films to teach technique, the boy said, as if her were a football coach reviewing a game tape.

"He would tell me what to practice," the boy said.

The boy said he hid the abuse from police and therapists at first, because he "didn't want to get them in trouble."

"I felt protective over my parents," the boy said. "I loved them."