The first clashes in January 1978 produced two deaths that were then commemorated on the 40th day in mass gatherings, which in turn produced new confrontations with security forces — and new deaths. Those deaths then generated another 40-day period of mourning, new clashes, and further deaths. The cycle continued throughout most of the year until the shah's ouster in January 1979.
The same cycle has already become an undercurrent in Iran's current crisis. The largest demonstration, on Thursday of last week, was called by opposition leader Mir Hossein Mousavi to commemorate the deaths of protesters three days after they were killed.
Again, because this a cultural and religious expression, it served – and may serve again – an unifying and organizing function for the disparately motivated Iranians who have taken to the street. Its power and efficacy should not be discounted nor overlooked. Indeed, Ayatollah Montazari has already called for another three days of mourning beginning Wednesday.
UPDATE: Karroubi has called for Thursday to be a day of mourning, according to AFP.