ISIS terrorists slit stomachs of mortally wounded victims on the floor. Eyewitness heard singular screams of torture without gunshots. Survivors hid in cellar for three hours listening to massacre above. Terrorists stabbed people in stomachs per trapped man's report. 89 people massacred at Eagles of Death Metal gig. Survivors Mariesha Payne and Christine Tudhope escaped by barricading cellar door. Men pleaded for wives' lives but terrorists told them to shut up. Attackers used knives and assault rifles on packed theatre. Victims left lying on concert hall floor. Police secured area after three-hour ordeal.