According to Torah, kosher mammals and birds are slaughtered by a special procedure called shechitah, in which the animal’s throat is quickly, precisely and painlessly cut with a sharp, perfectly smooth knife (called a chalaf) by a shochet—a highly trained.
An animal that dies or is killed by any other means is not kosher. It is also strictly forbidden to eat flesh removed from an animal while it is alive (this prohibition is actually one of the Seven Universal Noahide Laws, and is the only kosher law that applies to non-Jews as well as to Jews).
After the slaughtering, the internal organs of cattle are examined for potentially fatal diseases or injuries, such as adhesions (sirchot) in the lungs or holes in the stomach. The occurrence of any one of dozens of specified tereifot, as these defects are called, renders the entire animal not kosher.
Nikur (“deveining”) involves removing certain forbidden veins and fats from cattle. They are extremely prevalent in the hindquarters, and due to the complexity involved in their removal, this part of the animal is generally not sold as kosher.