Juan Cole explains the cultural significance of Mousavi's move:
Mourning the martyr is as central to Iranian Shiite religious culture as it was to strains of medieval Catholicism in Europe, and Mousavi's camp is tapping into a powerful set of images and myths here. The archetypal Shiite martyr is Imam Husayn, the grandson of the Prophet Muhammad, who championed oppressed Muslims in Iraq and was cut down by the then Umayyad Muslim Empire. Recognition that a Muslim state might commit the ultimate in sacrilege by beheading a person who had been dangled on the Prophet's knee has imbued modern political Shiism with a distrust of the state. When Husayn's head was brought to the Umayyad caliph Yazid and deposited before his throne, older companions of the Prophet are said to have wept and remarked, "I saw the Prophet's lips on those cheeks." Shiites ritually march, flagellate, and chant in honor of the martyred Imam or divinely-appointed leader.