The detailed narrative of the attacks by gas-filled barrel bombs dropped from helicopters, as recently as two weeks ago, comes from a report by a fact-finding team of the Organisation for the Prohibition of Chemical Weapons (OPCW), obtained by AFP.
"In courtyards, domesticated birds and animals died, and leaves on plants facing the point of impact withered and wilted 'as autumn leaves,'" said the report, dated Wednesday, which confirmed the systematic use of chlorine as a weapon in war-torn Syria.
The team interviewed 37 victims, medical staff and witnesses of the April attacks in northern Syria. These bombings were different from the high-explosive blasts the villagers were used to.
"When dropped, a piercing heavy, whistling sound – some comparing it to that of a fighter jet in a dive – would be heard before the barrel hit the ground," making a noise "more akin to high-impact crashes rather than to loud explosions", the report said.
"A dense, honey wax-to-yellow" gas then rose from where the bombs landed, survivors said.
"The cloud would rise to a height of approximately 60 to 70 metres (around 210 feet) and then settle, moving along the ground in the direction of the wind."
OPCW investigators were ambushed while heading for one of the attacked villages, Kafr Zita, in May and were therefore unable to visit to gather evidence.
Instead, they brought witnesses from their villages and interviewed them at a secret and secure location.
Syria did not have to declare its stockpile of chlorine – a toxic agent that can be considered a chemical weapon if used offensively – as part of a disarmament deal agreed last year because it is widely used for commercial and domestic purposes.
But it remains deadly.
"A child standing close to the impact site died later because of exposure to the toxic chemical, while showing none of the obvious physical trauma as that usually inflicted by a conventional explosive device," the report said.
President Bashar al-Assad's regime and the rebels fighting it have both accused the other of using chemical agents, including chlorine, in the bloody uprising that began in March 2011.
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There were over 200 casualties from one attack on the village of Talmenes, population 20,000, in Idlib province, on April 21 and 24.
"A woman, a teenage girl, and a seven-year-old boy died as a result of exposure to lethal doses," the report said.
Attacks on the nearby village of Al-Tamanah took place mostly at night.
"These attacks resulted in more than 150 casualties, and eight of the most severely affected, mostly women and children, died from exposure to lethal doses of the toxic chemical," the report said.
After an attack on Talmenes on April 21, "unsuspecting villagers attempted to escape to their usual shelter. The gas cloud also headed in the same direction, thus leading to the large number of casualties."
One family took shelter under the shower, while "others unsuccessfully tried to protect themselves using paper masks that are effective only against dust."
A sleeping toddler escaped serious exposure "because her face was covered with a blanket to protect her against insects."
The most recent reported attack was on the town of Kafr Zita, 30 kilometres (20 miles) from the city of Hama, on August 28.
The 37 witness accounts, as well as a "significant amount of supporting data," create "a distinctly discernible and revealing narrative," the OPCW said.
Several victims were evacuated from Syria, where some died.
Many first responders rushing to the scene of attacks were themselves exposed and required medical attention.
"The mere presence of victims in the hospitals made the entire premises smell strongly of a substance similar to what was variously described as bleach, cleaning material, or chlorine," the report said.
The OPCW said Wednesday it will continue to investigate fresh reports of gas attacks in Syria.