Havok would be nice. Also for bodies flying back being shot that's movie stuff. Its simple physics. If you fire a weapon and you do not fly back from the recoil then what ever the bullet/slug hits will not fly back either. They may jump a little from a shock reaction but that can be had from a bow shot and no one would expect anyone to "fly back" from an arrow HOWEVER that would be funny as hell to see in a zombie game. Most common reaction from being shot is the body drops like a sack of potato's and goes into shock and twitches a lot. "Death Spasms" and its not a pretty sight and IMO should be left out of games.