Much as the Gemara is concerned with milk that is found in an animal’s udder and requires that the udder be cut open to remove milk before cooking, the Gemara is also concerned about blood that is found in liver. Since an animal’s liver has large amounts of blood, ordinary salting is not enough to remove all of it. Here, too, the Gemara recommends cutting it open and squeezing it out.
The Gemara relates a number of stories that illustrate the disagreements about how liver is to be prepared. In one, Rav bar Shaba visited Rav Nahman‘s house and refused to eat the liver that had been cooked, leading Rav Nahman to insist that he be forced to eat, since it is inappropriate for a student to be more stringent that his teacher, certainly in his teacher’s own house. On the other hand, the Gemara tells of Rabbah bar Rav Huna who once visited the house of Rabbah bar Rav Nahman, who noticed that a liver together with its arteries had been prepared for the meal. He objected to this and explained to them that in order to prepare it for eating it would be necessary to cut it open lengthwise and breadthwise, leaving the cut part below to allow the blood to drain from it.
According to the ruling of the Shulhan Arukh (Yoreh De’ah 73:1-2) the common practice is to broil the liver even after it is cut open and drained, so that the blood will be totally removed from it before eating. Once the liver is broiled, it can be eaten, or, alternatively, it can be cooked in an ordinary fashion. The requirement to cut open and drain the liver only applies when the liver is whole. When it is cut up, then the only requirement is to broil it.