Palestinian protesters massed at a 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 protesters, 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 neighbouring village last month.
The Israeli border police called on them to disperse through loudspeakers, warning them they were near a "closed military zone."
Then the skunk truck arrived, spraying a cloud of yellow mist and filling the air with the suffocating stench of feces and urine.
More than one demonstrator said he preferred the tear gas Israeli troops usually use for crowd control, which sears the skin, nose, throat and eyes.
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 said.
"It protects the protesters because it doesn't require us to use tear gas and rubber bullets."