Story highlights Michelle Knight says Ariel Castro thought she was a 13-year-old prostitute

Cleveland kidnapping victim says she was tied up like "an ornament on the wall"

Knight, Amanda Berry and Gina DeJesus were kidnapped and raped by Castro

Castro committed suicide in his prison cell in September

Six months after she was freed from the "house of horrors" where Ariel Castro held her captive for 11 years, Cleveland kidnapping victim Michelle Knight is speaking out.

In an exclusive interview with Dr. Phil McGraw scheduled to air Tuesday and Wednesday, Knight describes a moment when Castro trapped her in a room and tied her up with an orange extension cord.

"I was tied up like a fish," she said, "an ornament on the wall."

An excerpt released by the "Dr. Phil" syndicated talk show Monday shows Knight sitting cross-legged on a couch and drawing a U-shape in the air with one finger as she describes how Castro hung her by her feet, neck and arms.

Knight also says Castro taped her mouth shut with duct tape, according to another excerpt posted on the show's YouTube channel . And she tells McGraw she once picked a lock to try to escape, drawing an ominous warning from Castro: "Now you're gonna be punished."

Knight, Amanda Berry and Gina DeJesus were freed from Castro's Cleveland home in May, drawing national attention to the horrific case.

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The dramatic rescue came after neighbors heard Berry's cries and broke down a door.

"It's astounding to me that she had the strength that she did," McGraw told "Anderson Cooper 360." "She says that she was referred to as the unbreakable one. She fought him every step of the way."

McGraw said Knight was chained around the neck and waist with a motorcycle helmet on her head. She was left there for days at a time, Mcgraw said, adding that Knight told him she couldn't lie down because the chain was too short. So she would just lean and wait until she passed out from fatigue.

Knight told McGraw, though, that she didn't always fight back, at least not at first.

She said she was in shock after being taken and all she could do was cry and beg him to let her go back to her son.

He threw money at her.

"He was obsessed with prostitutes and also he thought I was a 13-year-old prostitute," she said in the interview. "When he found out my real age he got mad."

Before the women's rescue, Knight's disappearance generated less publicity and attention than the kidnappings of Berry and DeJesus, and a level of mystery still surrounds her case.

But since their rescue, Knight hasn't shied away from speaking out.

"After 11 years, I am finally being heard, and it's liberating," she said in a powerful statement at Castro's sentencing describing the abuse she endured

"You took 11 years of my life away, and I have got it back. I spent 11 years in hell, and now your hell is just beginning," she told Castro. "I will overcome all this that happened, but you will face hell for eternity."

She said she was at the demolition site in part to remind relatives of abducted children that all is not necessarily lost.

"I want the people out there to know -- including the mothers -- that they can have strength, they can have hope, and their child will come back," she said.

Since their release, accounts have depicted Knight as someone who cared for the other victims during their captivity while also enduring great suffering herself.

A family friend of one of the victims said this year that Castro used Knight as his main "punching bag."

The friend said Castro hit Knight with a variety of objects, including hand weights. She has suffered vision loss, joint and muscle damage, and other problems from her time in captivity.

According to an initial incident report obtained by CNN, Knight said she became pregnant at least five times while in Castro's home.

When that happened, she told investigators, Castro "starved her for at least two weeks, then he repeatedly punched her in the stomach until she miscarried."

Knight said Castro ordered her to deliver Berry's child, according to a police source familiar with the investigation.

"What's most incredible here is that this girl who knows nothing about childbirth was able to deliver a baby that is now a healthy 6-year-old," a police source said.