After the ritual slaughtering or Shehita, the body of the animal is examined by the bodeq, the expert Rabbi who runs a virtual autopsy of the animal to detect any kid of terefa. "Terefa" means a disease which would have provoked that animal's death within twelve months. The Rabbis described seventy type of diseases /terefot that could affect an animal and therefore render it forbidden for consumption.
In practical terms most of these terefot are checked just when the animal presents a symptom. For example, if the animal is limping, the Rabbi would check the legs, thighs, hip, etc. to exclude an internal bleeding or the presence of any kind of a terminal affection. In general, however, the Rabbis would pursue animals with no symptoms of any disease.
Still, there is one organ that is always checked, particularly in cows: the lungs. Lungs are very sensitive organs because many times cows might swallow a nail, a piece of wood, etc. which might puncture their lungs and provoke a fatal disease. The lungs are checked for any accidental perforations in the same way the car's tires are checked for air leaking. Inflating them and submerging them in water. A leak will render the animal as terefa.
The Halakhic debate in this matter concerns the status of the animal when certain filaments (in Hebrew sirkhot) are found in the walls of its lungs. (This is avery technical issue, so I'm skipping some details). For Sephardic Rabbis those filaments are indicative of a perforation in the lungs and that animal is therefore declared "terefa". For Ashkenazi Rabbis, however, when those filaments could be removed, and the lungs do not leak, the animal is Kasher.
The presence of this type of lung-filaments is very common. Only 50% of all cows have completely smooth lungs (the word "halaq" means "smooth", lungs without filaments) while 80% of the other cows have removable lung-filaments. In other words, while for Sephardic tradition only half of all slaughtered cows will be considered Kasher (halaq) for the Ashkenazi tradition 90% will be considered Kasher.
(To be continued....)
And you thought you have seen it all....