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.
Both parents must carry a trait in order for a foal to be homozygous for that trait. For example, a sorrel bred to a black can NOT produce a foal that will be homozygous for black. A horse will throw it's color trait (dun, roan, etc.) 50% of the time unless it is homozygous for that trait.