(1) Your first question is not entirely accurate, as a quick perusal of the Halachic material regarding blisters on the lungs will indicate that sometimes they do cause Treifos (see Y.D. 37). You are correct that a scar will almost always cause a Tereifah, as it shows that the animal had a punctured lung. Every case is different. I have not found a clear answer to your question, but the Gemara later (55b) states regarding these very cases that one can never compare Treifos, since what for one organ is horrible, is fine for another organ.

(2) My conjecture is that whereas a blister on a lung might merely be a slightly bad blister which does not make a Tereifah, a pus filled blister may indicate that the kidney is not properly filtering the waste in the animal's system, which could lead to a quick death.

(3) Our website receives approximately 4 questions a day. However, some days we can receive as many as 10 - 15 questions.

Take Care,

Yaakov Montrose