Zombies
Zombies or better known as the undead, they wander the deserted streets of towns and cities or even the odd graveyard however you look at them their origins varies depending on what universe you look at movie or otherwise. In this case, they are from the video game/movie Resident Evil. The picture above shows a group of zombies travelling together as they roamed around the deserted streets of Raccoon City, they were once people of the city but were unfortunately infected with the T-Virus that broke out and spreaded throughout the city.
In the fanfiction found here, Codename Nightmare, the boys find themselves in a town that had been affected in the same way as Raccoon City with monsters roaming the streets crying out their hungry moans for fresh blood and flesh along with the other monsters that roam the streets of Newbay.
The infection varies into how it is passed from one person to another, as it could move from rodents into the water then into the humans of the city. The T-Virus once entered into a human slowly turns that person into a mindless zombie with only the basic of needs.
As the virus moves through the bloodstream, it shuts down the brain making the human victim agressive and act animal like. The early signs of infection are psychotic rage, persistant hunger and agressive behaviour to humans or other infected humans. It is important that the infected stays awake during the internal fight of the victim's body to help against the T-Virs, if the victim looses consciousness there is a high chance that the victim would not wake up until the transformation into a 'zombie' is complete, thus the loss of the human the victim once was.
To take down, or kill a zombie you would have to either shoot it seven times with a handgun or a direct attack to the head. Decapitating it in anyway or damage done to the spinal cord would also kill the zombie. When fighting a group of zombies, any method would do fine as long as its long spread a shotgun is suggested.