
Cambodians believe if they fail to honour the dead during the 15-day festival, which culminates Monday, the hungry ghosts will rise.
And this nation, with a bloody history of 30 years of civil war and the legacy of some 2 million people who perished under the 1975-79 Khmer Rouge regime, has many ghosts.
Those ghosts have recently already been raised, in memory at least, by the impending Cambodia-UN joint trials of former Khmer Rouge leaders, the first of which is expected within months.
The photographs of the five former leaders currently in custody are splashed across newspaper front pages almost daily.
Even though the majority of Cambodians were born after the ultra-Maoists were overthrown, and whose school textbooks remain bereft of any mention of the bloodshed in a government-decreed "spirit of reconciliation," almost everyone mourns some family member.
Ouk Bunna, 44, took nearly 30 years to venture back to the remote village where he last saw his father lying in a provincial killing field churned with blood and mud - and closed his dead eyes.
His mother died in a mortar attack on Phnom Penh by Khmer Rouge in 1973. His siblings, a brother and sister, starved during the long march to this village in Kampong Thom province, around 200 hundred kilometres north, after the victorious Khmer Rouge emptied the city.
The movement demanded everyone work in the fields in a drive to take Cambodia back to an agrarian utopia it called Year Zero, which claimed the lives of one-fifth of the population through overwork, disease, starvation, torture and executions in less than four years.
"Foreigners like to think the Khmer Rouge were all bad, but they don't understand that a lot of people in the countryside were forced to join or be killed," Bunna said.
In Buddhist Cambodia, there is always a ceremony at a funeral, and the pagoda will perform it for free if the family cannot afford it. There is always a photograph of the loved one.
But in April 1975, when Khmer Rouge troops took the city, witnesses say the streets of the capital were awash with family photos, and many people carry little more than memories of their lost children, grandparents, siblings, husbands, wives.
Most who died under the Khmer Rouge were never allowed to be mourned under a regime which outlawed religion, and ghosts unmourned are angry, hungry, restless ghosts, according to Khmer tradition.
"My father was tall, with white skin and a long nose," Bunna remembered on his way to the village - all highly prized traits in Cambodian society. He is short, dark-skinned, with a flat nose.
Bunna only has hazy adolescent memories but a clear recollection that everyone loved his father - except the new Khmer Rouge troops who entered the village that day before he turned 14 to take him.
He believes a member of his father's own family had informed them he was an educated former government official - a death sentence - perhaps incited by an ongoing family feud and promises of rewards.
But when he walks into the village, an old former Khmer Rouge woman washing a bowl of rice drops the bowl and screams his father's name. Then she realises it must be his son and comes running with joy. He realises for the first time that he is his father's image.
"When I had nobody, the village took me in. They loved my father. Everyone was hungry - not just the city people," Bunna said.
Former Khmer Rouge, who now say they denounce the things they saw under their former leaders, rushed from shabby huts to embrace a man they thought had died when he ran back to Phnom Penh in 1979.
Just up the road, a once-grand house stands empty and decaying.
"That was the village chief's home - that is where the orders to kill came from," Bunna says. The chief and his wife were themselves killed by angry villagers after the Khmer Rouge fell, villagers say.
And even in poverty, villagers shun the place rather than take one piece of expensive timber from where they say evil once lived.
The former Khmer Rouge villagers and Bunna, a prisoner they once took in as their own child, cry and talk about lost loved ones for hours, and then they talk about the festival of the dead.
"We will hold a ceremony for him when we have money," said one old woman, who can only offer green mangos now from a tree she and Bunna planted together under the guns of Khmer Rouge soldiers as virtual slaves together. "We want him to forgive us."
And Bunna says, "I think he already has," and there are more tears and incense as he leaves, driving past the place where he closed his father's dead eyes on his way back to the capital.
Later, on his way to the pagoda to honour the dead, Bunna tries to explain why Pchum Ben is more important to Cambodians like him than anyone who doesn't live with his history can express or know.
"We are a country full of ghosts, trying to heal," he says. dpa sl tl 280850 GMT Sep 08 nnnn//Deutsche Presse-Agentur/Bronwyn Sloan - September 28, 2008