The Palestinian protestors massed at the fence expected tear gas and rubber bullets; what they got instead was a putrid yellow wind, Israel's newest weapon against West Bank demonstrators.
The noxious mist, which Israeli police refer to as "skunk," was used for the first time earlier this month, when a truck-mounted cannon sprayed it over the heads of protestors, sending them racing down the hillside, retching and tearing off their shirts to try to escape the stench.
Dozens of Palestinians from the village of Bilin, along with international and Israeli activists, had marched to a nearby segment of Israel's controversial separation barrier to demand its removal, just as they have done every Friday for the last three and a half years.
"No, no to settlements; no, no to the wall!" they shouted, as they waved Palestinian flags and posters of Yusef Amira, a 16-year-old shot dead by Israeli police at a protest in a neighboring village last month.
Then the skunk truck arrived, spraying a cloud of yellow mist and filling the air with the suffocating stench of faeces and urine.
More than one demonstrator said he preferred the tear gas Israeli troops usually Israeli police say "skunk" is more effective at dispersing crowds than tear gas or the more lethal rubber-coated bullets, which killed Amira.
"It's the start of a change in tactics in dealing with crowd control and dispersing violent demonstrations and violent instances," Israeli police spokesman Micky Rosenfeld told AFP.
"It protects the protestors because it doesn't require us to use tear gas and rubber bullets."
It was inevitable, perhaps, that Israel would unveil the skunk in Bilin. The small West Bank village has recently spawned a growing protest movement pitting local farmers and international activists against Israeli police on a weekly basis.
"They use all kinds of violence against us but we have to get our land back. We are willing to sacrifice ourselves," says Ahmed Abu Rahma, a Bilin resident who has marched in the protests since they began more than three years ago.
The farmers have been galvanized by Israel's controversial separation barrier, a projected 723 kilometer (454 mile) stretch of concrete walls, barbed wire fence, and closed military roads, that snakes across the West Bank.
Israel says the barrier is necessary to prevent attacks on its cities and Jewish settlements while Palestinians say the fence, most of which is built on occupied territory, undermines the viability of their future state.
In September 2007 Israel's high court ruled in favor of village residents and ordered the barrier to be re-routed, but the military has yet to act, and the protests have since spread to neighboring villages.
In the nearby village of Nilin, demonstrators clash with Israeli troops weekly, with local youths bounding through the terraced orchards near the fence construction site, hurling rocks and scattering before tear gas grenades.
But in late July the violence spiked, with Israeli troops shooting dead a 12-year-old boy, Hamad Musa, and 16-year-old Amira within a few days.
Israel is investigating both incidents, and the deaths appear to have pushed the security forces to look into less-violent means of dispersing the protests.
Won’t be deterred
The new dispersal methods, no matter how unpleasant, do not appear to deter the protestors.
One of those marching on a recent Friday was Ashraf Abu Rahma who was shot in the foot with a rubber bullet in July by Israeli soldiers who had detained him. He was bound and blindfolded at the time.
The incident, captured on video by a fellow protestor, was widely condemned in Israel and seen as a further embarrassment for its security forces.
Abu Rahma, a relative of protestor Ahmed, said he had been hospitalised after taking three rubber-coated bullets to the same leg during a previous protest.
On Friday he limped up the hill, carrying a Palestinian flag into battle yet again.
"I am not afraid of anything," he says with a smile. "Not even death."