For Maria Gillespie, the memories of what she endured in a prison in Uruguay, when she was only 15 years old, are almost too much to bear.
She remembers being hooded, interrogated and tortured. Eventually every tooth was wrenched out of her mouth.
But she also remembers - as Amnesty International marks its 50th anniversary - how much she owes to the organisation that helped end the horror and set her free.
"I don't think that if I say 'thank you' it will be enough," Mrs Gillespie says of the Amnesty activists around the world who campaigned on her behalf.
"I think that I do owe them my life."
Amnesty was founded 12 years before she was jailed.
It called for collective action on behalf of those unjustly imprisoned around the world.
Maria Gillespie fell into that category after the military seized power in Uruguay in 1973, ushering in a period of severe repression.
She told the BBC Witness programme that although still so young, she was already married to a trade union activist who was wanted by the authorities, and had fled the country.
In his absence, and just a few weeks after the birth of her daughter, Maria was arrested.
She was accused of aiding the regime's enemies, and sentenced to 75 years in prison.
And so she began her solitary confinement in a windowless cell lit only by an electric bulb.
She described the noises that came through the walls: "People screaming. What sounded like people being dragged from one place to another, and then shots. And then everything went quiet."
She was repeatedly taken - with her head in a hood - for questioning about her husband's associates. But she knew nothing of his activities.
She had no answers for her interrogators.
"There was once when you could hear a child cry. And they said that was my daughter, and if I didn't help them something might happen to her - and I still couldn't help."
Eventually, every time she failed to answer a question, they pulled out one of her teeth.
They only stopped when she had none left.
"I lost them all," she said.
"Just awful. The pain. And unable to understand why. There was no need."
Then one day, extraordinarily, a guard handed her a postcard.
"It just said 'Dear Maria. Thinking of you. Margaret.' And an address in Scotland."
She told the guards the card could not be for her because she didn't know anyone in Scotland. But they insisted it was indeed addressed to her.
A few days later another card came, this time from France. Then one from Canada. The next was from the United States.
Soon they were coming in a torrent.
At one point the guards said they would give her just some of the latest to arrive. They then handed her 900 cards.
Maria kept noticing the words Amnesty International on the cards. She had never heard of the organisation, and could not understand why the cards were coming.
She worried that Amnesty might be some sort of Communist group, and feared that its support might get her into even more trouble.
But the authorities were buckling.
Perhaps they were uncomfortable with the idea that decent people around the world were looking on while they tortured a 15-year-old girl.
Eventually Maria was shown a room half filled with sacks of mail addressed to her.
She was left in no doubt that all this attention had become a problem, and she was released after a year.
But Maria was forced to leave Uruguay immediately and put on a boat to Argentina.
On the streets of Buenos Aires she saw a sign on a building bearing the words she had seen on the cards, Amnesty International.
She made contact with Amnesty activists, and gradually began to understand how the organisation had rescued her.
Later, Maria was given asylum in Britain and re-united with her husband and daughter.
She has since re-married, and today Maria Gillespie lives in Chester, in the north-west of England.