Virus is a microscopic organism that lives in a cell of another living thing. Although viruses are extremely small and simple, they are a major cause of disease. Some viruses infect human beings with such diseases as measles, influenza, and the common cold.
Passive Mobs. Passive mobs are composed of creatures that will never, under any circumstances, attack the player. Some passive mobs can be bred to create more of them, e.g. pigs can be bred to effectively farm them.
Farming mobs in minecraft can be a great way to collect huge amounts of resources with little effort, besides the effort put into building the farm of course. Most farms rely on the spawning mechanisms of mobs, though other farms use mob spawners found in dungeons and abandoned mineshafts.