SANA'A // After Friday prayers, about 25 protesters stood outside Sana'a University chanting for President Ali Abdullah Saleh to resign. As the clock ticked towards 1.30pm, one by one, they began to leave, as did a small group of people watching them.
"They've gone to chew khat," Shihab Sharabi, 21, one protester, said with a sheepish smile.
Add khat, a leafy narcotic consumed by virtually everyone here, to the many reasons Yemen's popular uprising has yet to gain the same momentum as the revolts in Egypt and Tunisia.
For the past three weeks, protests have rocked this impoverished capital. Some were massive; others were small. But one thing has remained constant: they all ended before 2pm. That is when most Yemenis enter khat-chewing sessions in their homes or cars, or practically anywhere.
Samir al Sami, an aid worker observing the demonstration, said: "In Yemen, chewing khat is like drinking water. We can't live without it."
Khat is said to induce euphoria, loss of appetite and sleeplessness. The World Health Organisation classifies it as a drug that, if abused, can cause mild psychological dependence. It is an illegal substance in the United States.
In Yemen, researchers estimate that as much as 80 per cent of the population chews khat leaves, the vast majority starting at a young age.
That confounds the opposition legislator Aidroos Al Naqeeb. Asked why Yemen, inflicted with many of the problems fuelling the rebellions in Egypt and Tunisia, has not experienced a similar transformation, Mr Naqeeb cited Yemen's weak civil society and weak culture of popular protests.
Then he added, shaking his head, "The culture of khat is also playing a role."
Student Khalid al Hamri, 22, said it would be pointless to protest in the afternoon. "In the morning, all the government officials are in their offices. They will hear our protests," he said. "In the afternoon, nobody will listen to us because everybody is chewing khat."
Just then a man walked by, his left cheek bulging with khat. He glanced at the protesters and jeered: "Don't you have anything better to do? The government will put you under its shoes." Then he walked in the direction of stores selling khat.
At the shops were much bigger crowds, some spilling onto the street. Everyone was clutching small plastic bags containing the leaves.
Back at the university, the protesters sat on the sidewalk, clutching Yemeni flags. Mr Sharabi vowed that if Mr Saleh did not step down, they would protest all day, until midnight.
"We will bring our khat here and make a revolution," he said, as another protester walked towards the khat stores.
* Washington Post