The seven-inch scar runs diagonally across the left flank of his skinny torso, a glaring reminder of an operation he hoped would save his family from debt but instead plunged him into shame.
Chhay, 18, sold his kidney for $3,000 in an illicit deal that saw him whisked from a rickety one-room house on the outskirts of the Cambodian capital Phnom Penh to a gleaming hospital in the medical tourism hub of neighbouring Thailand.
His shadowy journey, which went unnoticed by authorities two years ago, has instigated Cambodia's first-ever cases of organ trafficking and the arrests of two alleged brokers.
It has also raised fears that other victims hide beneath the radar.
At the corrugated iron shack he shares with nine relatives, Chhay says a neighbour persuaded him and a pair of brothers -- all from the marginalised Cham Muslim minority -- to sell their kidneys to rich Cambodians on dialysis.
"She said you are poor, you don't have money, if you sell your kidney you will be able to pay off your debts," the teenager told AFP, requesting his real name be withheld.
Identical stories have long been common in the slums of India and Nepal, better-known hotspots for traffickers. Up to 10,000, or 10 percent, of the organs transplanted globally each year are trafficked, according to the latest World Health Organization estimate.
But on discovering the broker earned $10,000 for each kidney they sacrificed, the donors filed complaints, alerting police in June to a potential new organ trade route.
"Kidney trafficking is not like other crimes… If the victims don't speak up, we will never know," said Phnom Penh's deputy police chief Prum Sonthor.
In July his force charged Yem Azisah, 29 -- believed to be a cousin of the sibling donors -- and her step-father, known as Phalla, 40, with human trafficking.
The pair are being detained and await trial.
- First case -
Trafficking is a widespread problem in impoverished Cambodia and police routinely investigate cases linked to the sex trade, forced marriage or slavery -- but this was the first related to organs.
“This is easy money that earns a lot of income, so we are worried," said Prum, adding there were at least two other Cambodian donors taken to Thailand who had not filed complaints.
The complicity of donors, whether compelled by poverty or coerced by unscrupulous brokers, makes it an under-reported crime which is difficult to expose.
In August media reports emerged about new alleged organ trafficking cases at a military hospital in Phnom Penh.
Prum, who investigated the case, said it was a training exercise between Chinese and Cambodian doctors, using voluntary Vietnamese donors and patients.
But he was unable to rule out whether money changed hands.
- 'I regret it' -
Chhay watches from the sidelines as boys his age play football, two years on from an operation that has left him feeling weak, ashamed and still in debt.
"I want to tell others not to have their kidney removed like me... I regret it. I cannot work hard any more, even walking I feel exhausted," he said. In July he started work at a garment factory.
Little research has been done on the impact of transplants on paid donors like Chhay but the WHO has reported an association with depression and perceived deterioration in health, highlighting the lack of follow-up care.
Chhay remembers few details of a transaction that still haunts him, claiming no knowledge of the Thai city where he was taken or the woman he sold his kidney to.
In Thailand health authorities are trying to shed more light on the murky trade, with several Bangkok hospitals under investigation.
Focus has fallen on the documents traffickers forge to prove donors and recipients are related -- a requirement in many countries where it is illegal to sell an organ.
"We've asked hospitals to be more careful" when checking documents, Thai medical council president Somsak Lolekha told AFP, adding his organisation was reviewing its transplant regulations.
- Tip of iceberg? -
Driving the demand for a black market in organs is the globally soaring number of sick patients waiting for transplants, especially kidneys.
In Thailand alone there were 4,321 people on the organ waiting list up until August with deceased donors' organs forming around half of the 581 kidneys transplanted last year, according to the Thai Red Cross Organ Donation Centre (ODC).
World over this increasing reliance on living donors has left desperate patients scouring for volunteers in their families, or, in some cases, recruiting underground.
Prompted by concerns over trafficking the ODC, which oversees organ donations, launched a pilot project in April making it compulsory for hospitals to provide them with details of living donors.
"Before they could come to Thailand without our knowledge... We are concerned about hospitals where they are not following rules, that's why we asked for a register of living donors," said ODC director Visist Dhitavat.
While regulations are being tightened experts fear the booming medical tourism industry in Thailand, reputed for high-quality but low-cost care, could give rise to more criminal networks cashing-in on the vulnerable.
"It could be the tip of the iceberg," said Jeremy Douglas, United Nations Office on Drugs and Crime representative for Southeast Asia and the Pacific, on the recent Cambodian arrests.
"There could be a lot of others (cases) that aren't just simply coming to trial."