Islamic State uses it as a punishment. It's wielded by the female division of the "hisba" moral police to keep other women in line. If you curse IS, wear revealing clothes or speak to a man who's not your husband, you will be bitten. It usually leads to the victim's death. The ghoulish women who wield this instrument are often Russian or Chechen.

Or so people say.

The problem is that no one can agree, exactly, on what the biter is. And nobody I can find in Mosul itself, or in northern Iraq's displaced people's camps, has actually seen one.

Everyone has heard of it, but no one can point me to anyone who has suffered its terrible pain.

I first hear of the biter from Maher*, a father of four in Qayyarah Airstrip camp.

"It's an electric device that bites women on the chest," he says confidently. "The repercussion is that a lot of ladies have their breast removed ??? or die."

Maher believes the cause of death may be cancer, but he can't be sure. Another biter victim, though, "went crazy and fled the town. She died from the infection in the wound".

Horrified, intrigued, I ask around.

A few days later, in Khazer camp, another man, Samad* tells a slightly different story.

"It's a set of teeth," he says. "They put it in their mouth and it's made of iron."

Samad says one woman he had heard of was swearing about IS so loudly inside her own house that her curses could be heard on the street. IS sent a biter who fitted the ghoulish instrument into her mouth then tore into the woman's upper arm.

"The woman who got bitten is about 35 years old," Samad says. "The biter was wearing a burka: we couldn't see her. They took the bitten woman to hospital."

Online the biter looks different again. A picture in the Daily Mail resembles a gardening tool. It's actually a 15th-century torture instrument called the "Breast Ripper", housed in a German torture museum. A story on Russian fake news site Sputnik, also lifted by the Daily Mail, says it is used on children, who often bleed to death as a result. The Independent carried a story, without a picture, of a woman saying her sister had been a victim.

'THE BITER' The device shown is a fifteenth-century Breast Ripper, and is kept in the torture museum in Germany. Photo: Supplied

To the people in the camps, who have recently fled IS, the idea of the biter is real and terrifying, even if they have never seen one.

Samad says a local militia unit had caught a woman with the instrument, and she had somehow grown rich from the work. She had $US240,000 with her, he says.

Another man in Khazer camp, Ibrahim Ismail Abdullah, tells us a woman biter was caught trying to hide among civilians on the other side of the camp. He did not know her name.

But the accounts keep changing. Asked about biters, Yusuf Abbas, a resident of Mosul, tells how a nine-year-old girl died after she was punished for wearing a T-shirt and a dress that showed her legs. Instead of biting, though, she was pinched.

"They pinched all the parts of her body that were exposed," Yusuf says. "Their hands were big and strong, and the girl died that night from fear and pain.

"The women say the girl was poisoned. I don't know how; I just heard she died in the night."

The medical facility at Khazer camp has responsibility for the health of 38,000 traumatised and sometimes horribly injured people. Here, hundreds of displaced people every day present their wounds and illnesses for treatment or referral.

Saddam Saleh is the administration assistant manager who decides what cases get the ambulance to the hospital in Erbil, 80 kilometres away. We ask him about the biter.

"I haven't seen a single case," he snaps. "It's propaganda. It may be a few cases, but it's been blown up."

So is the biter a myth or a nightmarish reality? And if it is a myth, did IS create it deliberately to terrify people?

Like many, Fazila Sarhan, 57, tells us in her Mosul house that she has heard of it but has never seen one.

"Do you believe it?" I ask.

Her answer is firm.

"Anything I hear about IS, I believe."