Keyhacktoggle unlimited health, toggle no reload, toggle unlimited ammo.
Most old civilizations had the costume of building temples or even raising a great monument for their divinities, usually offering sacrifices from time to time to make sure they would keep them happy. However, it was hard for them, as it is today, to figure if the praised entity has good intentions at all. Making a mistake didn't offer much trouble to them in the past, but now the result of their adoration to demons resulted in revived corpses walking and looking for flesh.
Avoid them by jumping with Space-bar, crouching with Ctrl, shooting with the Mouse and walking with the WASD keys.