the knife creased the cloth of his field jacket and , once above his chest , bourne spiralled the arm downward , twisting the wrist now in his grip , crashing his shoulder into the assassin 's body , yanking again as carlos plunged sideways off balance , his arm pulled half out of its socket jason heard the clatter of the knife on the floor ; he lurched towards the sound , at the same time reaching into his belt for his gun .