SHOVELLING human waste was one of the most coveted posts for prisoners in Auschwitz, says the guide, pointing to the circles carved out of wooden planks that counted for toilets in this dank barracks.
The Nazi guards here in Birkenau, she explained, would by and large leave the "shiessekommandos" alone, afraid of catching some nasty disease.
It is far from the worst remnant of horror the downcast Croydon sixth-formers looking on have been shown today, nearing the end of their tour of two Nazi concentration camps; red-bricked Auschwitz and its crumbling sister, Birkenau.
They have already seen a cabinet filled with 1,950kg of human hair, shorn from prisoners' heads and sold on to factories where it would be used to stiffen soldiers' uniforms.
They have seen a mountain of prosthetic limbs and wheelchairs robbed from newcomers; hooks on which prisoners were strung up; and a firing wall where they were shot.
And they have stood inside the concrete walls where prisoners thought they were having a shower, until the cyanide gas was switched on.
"This man here was just sentenced to death," they were told by Polish guide Dorota Cieplinska, pointing at a photo of a man at the head of a long line.
Ms Cieplinska has been leading these tours for 20 years, and still sounds upset when detailing how the more than one million people, mostly Jews, died here during the Nazi Holocaust.
The Holocaust Educational Trust (HET) has flown 200 schoolchildren from south London and Kent here today (last Thursday), to make sure the "lessons" of the Holocaust are not forgotten.
It is one of many regular trips it runs for schoolchildren across the country, always joined by Rabbi Barry Marcus of the Central Synagogue in London.
They have a £1.5 million government grant for the Lessons from Auschwitz project, and schools or students are charged less than £60 each.
It might be hard to learn when the main impulse is to run away, but the trip has certainly sparked questions among the wide-eyed schoolchildren.
On the plane back to Gatwick, Olivia Cope, from Croydon's Brit School, recalled clambering to the top of the watchtower overlooking Birkenau.
The roughly one square mile of barracks, cemeteries and gas chambers was mostly destroyed by retreating Nazis in 1945.
What is left is mainly rubble, birch trees – and one's imagination to fill in the details.
Olivia, 18, said: "I had no idea how big Birkenau was. It really brings it into perspective. And walking around just felt so eerie. I cannot believe this was allowed to happen."
Celiya Koster-Brown, a fellow Brit School student, was also grappling with the scale of the place. The 18-year-old said: "It surprised me how big the camps were – how all this work went into killing people.
"I found it harder than I thought it would be to imagine the people there.
"But I learned so much more about the conditions they were kept in."
Riddlesdown Collegiate student Gil Yehezkel, whose family's history was caught up with that of the Holocaust, had been struck by the mountain of prisoners' shoes on display at Auschwitz.
The sixth former – whose Iraqi-Jewish grandparents left Iraq in the early 1940s for what became Israel – said, sadly, that the shoes' many styles reinforced that the prisoners being Jews was their binding feature.
Benjamin Flook, from Purley, meanwhile, said his investigations were just beginning. "I am interested in the history and it was one of the darkest events of man and something I wanted to investigate further," said the 16-year-old, who attends Wilson's School in Sutton.
"It was more sort of humanised than I thought it was, through the hair and the shoes."
He added he was "affected" by the closing speech of Rabbi Barry Marcus, who warned of the universal threats of racism and prejudice.
Benjamin said: "I was quite affected by that. It shows how if no-one stands up against something, what can happen as a result of that."
Sutton High student Eleanor Trefusis was also dwelling on that thought.
The 17-year-old, from Purley, said: "One of my main things was to find out about why the British did not intervene with what happened.
"It is often overlooked – you tend to forget how maybe it could have been stopped."
The trip had partly helped her enquiries, she said, adding: "[Our guide] was saying how the main aim [for the British] was to win the war, and the Holocaust did not directly affect that."
She added: "I was looking at it more from a religious studies perspective.
"I am also interested in how people feel about ending lives, because I just like looking deeper into why people feel they have the right to take people's lives."Rabbi Barry Marcus, of the Central Synagogue in London, accompanies each of the regular trips to Auschwitz-Birkenau made by the Holocaust Educational Trust (HET) every year. He said he started running day trips to the camps in 1994, working mainly with the Jewish community until he was approached by HET. The Rabbi said: "It gave me an opportunity to be exposed and to also have the wider community exposed to the Holocaust from a Jewish viewpoint. "It is not the case that it only relates to or threatens Jewish people – intolerance, hatred and racism threatens everybody." Rabbi Marcus used his closing ceremony to warn of the importance of people standing up for others. He also spoke of present-day anti-Semitism, and claimed the leader of Iran had been 'threatening another Holocaust', referring to President Ahmedinejad's speech last year at the United Nations. Speaking on the plane on the way back, Rabbi Marcus, an advisor to Chief Rabbi Jonathan Sacks, said he believed Iran was a 'massive' threat. He said: "If a few marginal people are making anti-Semitic noises ok, it is unpleasant. "But when a head of state is given a platform (at the United Nations) that gives it a sense of respectability. "He denied the Holocaust but at the same time threatened to wipe out Israel and it goes all over the world, so we are nervous." He added: "At the moment increasing the sanctions on Iran [is the way to deal with it], but we are fearful that the next Holocaust will be, if, God forbid, there will be one, the killers will never see the whites of the eyes of their victims. "Because it's a whole new game pressing a button releasing hundreds of nuclear weapons on people, hundreds of thousands of miles away but equally as destructive." Israel is the only nuclear power in the Middle East. HET has taken more than 17,000 students and teachers to Auschwitz-Birkenau since 1999. Last Thursday's 'Lessons from Auschwitz' trip included two students each from Coulsdon Sixth Form College, the Brit School, Harris Academy South Norwood, Riddlesdown, Trinity and Old Palace. Students also heard from a Holocaust survivor before the trip, and will attend a seminar this weekend to discuss their experiences. They also give presentations on their experiences to their schools. HET chief executive Karen Pollock said: "The Holocaust Educational Trust's Lessons from Auschwitz Project is such a vital part of our work because it gives students the chance to understand the dangers and potential effects of prejudice and racism today."