As my colleague David Kirkpatrick observed in an interview on Thursday, the yawning political divide in Egypt stems from a kind of “national identity crisis — so debates aren’t just about a matter of policy, they are about ‘Who we are.'”

The deadly street fighting on Wednesday started after Islamist supporters of President Mohamed Morsi descended on a small number of protesters staging a sit-in outside the presidential palace, destroying their tents and chasing them away from the territory they occupied after tens of thousands of protesters swarmed the area the night before.

On Thursday, opposition activists pointed to a single frame of video that seemed to them to encapsulate the threat they face from the president’s Islamist supporters. The frame, taken from raw footage of secularist protesters being chased from the palace walls by Islamists chanting “Morsi! Morsi!” showed a man clapping his hand over the mouth of a veteran female activist, Shahenda Maklad.

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The video, posted online by El Watan, a Cairo news site, shows that Ms. Maklad, 74, was in the process of shouting, “We are the Egyptian people!” when the man physically silenced her.

Earlier this year, after Ms. Maklad led a women’s march to Tahrir Square, to protest the sexual abuse of female protesters by Egyptian officers, she told the news site Al Akhbar that she was not worried by the Islamists’ electoral success. “Their victory was merely a matter of seizing the right moment in history,” she said.”They exploited people’s poverty and their distorted awareness. The people will eventually awaken from this state of confusion. It is good for the people to try Islamist rule now, because they are drained.”

Late Thursday, after Mr. Morsi blamed his opponents for the violence in a defiant speech, his opponents pointed to another shocking image, showing the appearance of a young activist named Ola Shahba who said in an interview on a private television channel that she had been badly beaten by the president’s supporters the day before.