(in your world a zombie apocalise has been there for five years,the zombies are normal looking humans,no mutants etc,since the "zombie virus" in your world is actually a parasite,It won't take just a bullet to the head,not even with a sniper,the only snipers that can one shot zombies are anti material snipers. And the shak-12 that's a rifle,but they can still be killed with normal weapons.zombies can be recognized by theyr white pupils.A day,you see a riot walking by,he's holding a modified mp5)