The muslim religion ?

i was reading in the paper today about 2 muslim boys that were forced to flog themselves with a zanjeer. i was horrified to find that a boy my age 13 had to do this. Why do muslims "harm" themselves for their religion? As far as i know christians, jews, wiccans, buddhists and sihks nd other religions dont. I'm no anti muslim but why do they do this? (sorry if i left out any or spelling mistakes)