Taboos in Madagascar's rural tribes are part of the fabric of society, ranging from the mundane, like not planting rice on a Thursday, to the practical, like not having sex with a sibling.
But one taboo is causing widespread misery amongst mothers and children on the southeast African island, the taboo of raising twins.
Now a new Channel 4 documentary examines how the children and mothers become outcasts, with raising twins compared by tribal elders to eating faeces.
The Mayor of the town is campaigning to challenge the "taboos" that villagers believe, but in tribal villages with no electricity, let alone access to television news, the message is hard to get through.
"No one is really sure how the taboo began," journalist Kiki King told HuffPost, "but it is so ingrained in the culture it is almost impossible to challenge."
Ursula, the mother of two twins, Giovanni and Venua was told by her husband to abandon them. “When my mother fell ill and died everyone said that her death was her punishment because she didn’t respect her culture - the ancestors," she told the reporters.
Carolin gave birth to three sets of twins, and has been forced to move house around thirty times because her neighbours feared the twins. Now, she lives in a tiny tent in what amounts to a small refugee camp for twins and their mothers.
King said she was initially nervous about seeming to criticise the belief and culture of the tribes in Madagascar. But she changed her mind upon meeting the women there. "We tracked down and found the mother of one of these abandoned twins, a 20-year-old woman living in a remote village with no electricity, running water or sanitation who told me she was 'terrified' when she gave birth to twins."
One family made a particularly deep impression on King. "I met the mother of one woman who had given birth to twins and she said 'we don't have a choice', it is the tribal elders that decide. That made me realise that it is a group of old men that decide the fate of these children."
Meeting the tribal elders was a shocking experience. Asking them why they believed it was taboo to raise twins, King got a troubling response.
"They laughed at me and said, 'to us, asking us to raise twins is like asking us to eat our own shit'. We got that translated by two different experts. That is what they said."
“As long as we are still alive we are not going to dilute our ancestral culture…we have a saying - that anyone who keeps twins has no soul," one other elder told King.
"Most twins are abandoned in this part of Madagascar, but it makes them more likely to be adopted abroad," King said.
Through centres such as CATJA, where the crew filmed, twins are placed for adoption, usually going to start new lives in France, Sweden, Italy or Canada. A few are also adopted locally, sometimes informally amongst villages and extended families who don't belong to the same tribe, or are wealthier and more educated.
"I met two women who adopted this way, and what struck me was how normal it was for them to breastfeed their adoptive babies," King said. "Neither woman was already lactating, and neither had had children of their own.
"While one was just starting out, the other told me this was completely normal, she brought on breast-milk after a few weeks and described how she did it.
'It struck me as extraordinary that in a place where formula milk is prohibitively expensive, something which I had only heard about as a mummy-vine myth was so utterly and completely normal."
Channel 4's Unreported World- The Cursed Twins is on Friday at 7.35pm