Christian-Muslim violence in Cairo threatens to spin out of control. Twelve people dead yesterday, two churches burned, and no particular reason to think the government can put a lid on it. It's terrible, and also fascinating to see how the violence unfolds. Over the weekend, it unfolded the old-fashioned way -- with a rumor that Christians were holding a Muslim woman against her will: Here is part of David Kirkpatrick's report:

Like many recent episodes of Muslim-Christian violence here, the strife started with rumors about an interfaith romance and a woman's abduction. According to a police report, a Muslim named Yassim Thaabet Anwar from a city up the Nile had come to Imbaba looking for his wife. He said she was a former Christian from the neighborhood who had converted to Islam in 2010 but had recently disappeared. And he asserted she had been kidnapped and held in the Church of St. Mina against her will -- a pattern of allegations that has recurred in several recent high-profile episodes of sectarian conflict.

Christians in the neighborhood said that there was no such woman in the church, and, by Sunday night, the local police and government officials agreed.

But early Saturday evening, Christian men in the neighborhood began receiving phone calls from friends warning that a group of Salafis was approaching the church. More than 500 raced to defend it, armed with sticks, knives and other makeshift weapons, according to Christian residents and the police report.