전도서 10:7 할라카: Shulchan Arukh, Yoreh De'ah

The Laws of Checking Lungs (25 sections) 1) One need not proactively check (without cause to assume there would be an injury) any part of the animal for treifot (specific terminal injuries) except the lungs of domesticated and wild species of mammals to see if there are any sirchot (strands of connective tissue). Anyone who "breaches the fence" to eat meat without checking the lungs should be bitten by a snake. Rema- We have the custom to also inflate every lung, even if there is nothing wrong with it. In some places they are lenient and don't inflate the lungs unless there was a sircha removed by rubbing, and this is the main understanding.