Zanjir Matam Muharram, where some Shia Muslim men will ceremonially beat themselves and swing chains with knives attached, in remembrance of the death of Imam Hussain, the grandson of the Prophet Muhammed. Lahore, Pakistan. 26/12/2009.

Today is the 8th of Muharram the first month of the Islamic calendar, Muharram is a very important month for Shia Muslims because on the 10 of Muharram Imam Hussain the grandson and family (consisting of 72 people) of the Prophet Muhammed were killed by an army of between 20,000-30,000 at the Battle of Karbala on the orders of Yazid because Hussain did not accept him as Caliph and was not willing to take the oath of allegiance. in Muharram the Shia mourn their Imam and his death, a celebration of justice over evil.

I agree with wikipedia's description of Matam which is "Many of the male participants congregate together in public for ceremonial chest beating (matam) as a display of their devotion to Imam Husayn and in remembrance of his suffering. In some Shi'a societies, such as those in Bahrain, Pakistan, India, Afghanistan, Lebanon and Iraq, some male participants incorprate knives or razors swung upon chains into their matam. This practice is permissible by major Usooli Ayatollah such as Muhammad Shirazi and Sistani, however some major scholars such as Khameini have banned it in Iran temporarily, while others such as Fadlallah deem it permanently impermissible. In general however, the act is controversial."