Aid workers dealing with the problem in neighbouring countries call it "the horseshoe".
Serb commanders wanting to rid a Kosovo town of its population assemble paramilitary forces in a rough horseshoe-shaped ring around it. The men involved then move in, and are allowed to indulge their appetite for killings, beatings, burning, looting, and any darker desires, with only one rule - do not close off the exit road.
There is method in this operation, which may go down in history as the most efficient mass deportation of people seen in Europe this century .
Bosnia's war may have added the phrase "ethnic cleansing" to the world's lexicon, but Kosovo has seen it refined and improved. Serb forces took five months to move one million Croats and Muslims in Bosnia in 1992. Serb forces in Kosovo have moved more than 800,000 in just four weeks.
This is how they do it.
The first step is to assemble the force. Paramilitary gangs move in, including some recruited by Arkan, the Belgrade-based warlord who pioneered "ethnic cleansing" in Bosnia with his private army, the Tigers. But paramilitary has come to mean any group of armed men willing to, often eager to, attack civilians.
Many are simply local men. "One day the guys are laughing and joking with us, the next day they are beating my father," said 15-year-old Mendurim, who has fled Pristina.
Backing them up, usually from a distance, is the army.
Then come the police. Refugees testify that once they are on the move, the paramilitaries disappear. Instead, routes are marked out by traffic police, barking orders for the refugees to keep moving and avoid side turnings.
The aim here is to keep the people moving - any attacks on the moving columns may only split them up, with the people fleeing in all directions.
As they wait to cross a border, often for days, in traffic jams 20 miles long, the paramilitaries and police arrive once more for a final bout of looting and occasional molestation. Baton Haxhiu, editor of the leading Albanian newspaper, said while he waited to cross into Macedonia in a queue of cars for four days, two women were dragged out of a car behind his, raped and brought back later that day.
"It's very controlled - in the village those guys are told, don't go ripping them off now, because we want to keep them moving," said John Fawcett, head of the Tirana office of US-funded lobby group International Crisis Group. "But later, by the border, the message to them [the paramilitaries] is `you did your job, now get your pay'."
Who controls the operation is unclear - though Western diplomats say it is likely to be President Milosevic, who co-ordinates the activities of his military, paramilitary and police units.
This "ethnic cleansing" is performed in waves. It began the week before NATO's air offensive, launched on March 24th, with attacks on the northern Cicavica mountain, a rebel stronghold overlooking a key highway from Pristina to Belgrade.
In a single day half a dozen villages were bombarded - and once their inhabitants had fled, local Serb civilians, watched by astonished international monitors, moved in to steal what they could, and burn what they could not.
But the NATO bombing saw the real outbreak of savagery. The morning after bombing strikes hit targets in Kosovo and Serbia, apparently spontaneous shootings and arrests took place across the province.
The first stage of "cleansing" was in the west and south, with a string of towns being emptied.
The north-eastern town of Pec was ransacked, and its people pushed into Montenegro. To the south, Orahovac, Suva Reka, Djakovica and Prizren were also emptied - freeing the vital "corridor" highways through which successive waves of Albanians would be herded over the coming weeks.
A variation in this tactic was used in the southern Drenica region, long a guerrilla stronghold. Here a huge circle of army and paramilitaries was formed around villages. Then the attacks began.
These attacks forced the villagers inwards towards the centre of the circle, a process that took three days as one village fled into another which was itself "cleansed". By the third day tens of thousands were gathered in a single town, Malisevo, where buses appeared to drive them to the border with Albania.
Once the main roads and border towns had been emptied, the "cleansers" moved deeper into Kosovo. The town of Mitrovica was emptied - but they ran into problems when NATO bombed a bridge through which 3,000 refugees had already passed.
Instead, and with great swiftness, police organised a new route, one that forced the refugees into a forced march across the northern top of Kosovo, then down through Djakovo.
But after 10 days, the Serbs suddenly stopped the process. Even in reverse gear, the system has worked well - if that is the word. Refugees from the Srbica area say they spent three days being marched to the town of Djakovo, only to be suddenly turned around to spend another three days walking back to where Serb police had already found a schoolhouse near the village of Llausa to house them.
Another three days went by, until the police came again and told the refugees, all women, children and the old - the men had fled to the hills - to move once again. It was another five days before they were finally to cross, exhausted, into Albania.
Finally came the "cleansing" of the capital, Pristina. For 10 days, residents reached by phone or email told of the town being chopped into sections by police roadblocks, and of hearing shooting day and night.
Then, section by section, the police went door to door, ordering people into the streets. Some took to their cars - fine, unless the police decided they liked the make of car. Others simply walked, in long columns that stretched along the main highway out of town to the railway station at Kosovo Polje. Here trains, then buses, took them south to Macedonia.
But the Serbs appear keen to keep at least a part of Kosovo's 1.8 million ethnic Albanian population as "human shields" in the event of a NATO attack. And it is these people that aid agencies fear for - pushed from one place to the other, under terrible stress, without food or medicines.