Why does cheese have holes ?

Yesterday I was watching Tom and Jerry cartoon show on t.v. . There Jerry mouse was eyeing on a piece of cheese . That piece of cheese was having holes in it. As I am a keen observer of such silly things , I began to wonder why does cheese have holes ? The holes are made by the bubbles of gas produced by bacteria in fermentation process . When this fermentation process is carried out , long molecules of cheese are broken down into small , simpler and tastier molecules by the action of enzymes . At the same time , bacteria will produce carbonic gases which will result in the formation of holes just like our dosa .