I've actually used a katana on those ballistic dummies that simulate real flesh/bone. As a normal untrained person I can guarantee you wont be swinging the blade with much force at all after the 5th zombie. Sure they can slice through flesh like butter. But what about the bone? Thats a much different story my friends...Not to mention the stress it would be putting on your fingers, they'd get extremely sore eventually. Then at that point your fingers would be so stiff you couldnt even pull a trigger on a gun, which means you're about to get wtfpwnt