What are the defects and traumas that render an animal a treifa? The Mishna lists various categories, such as a perforated gullet, a severed windpipe, a perforated brain membrane, a perforated heart chamber, a broken spine and a severed spinal cord, a completely removed liver, as well as various perforations or tears to the lungs, stomach, gallbladder, small intestines, and rumen. The list also includes severe external trauma, such as falling from a roof, having a majority of the ribs broken, or being clawed by specific predators. The Mishna establishes the overarching rule: any animal afflicted with a defect or injury such that a similar animal cannot survive is deemed a treifa.

Resh Lakish derives the principle that a treifa cannot survive from the verse, "These are the living things which you may eat," teaching that only an animal capable of living is permitted for consumption, whereas one that cannot live is forbidden. Conversely, the opposing view holds that a treifa can survive, deriving from the same verse that a specific type of animal that is capable of living is permitted for consumption, while another animal that is capable of living (the treifa) is forbidden. However, after the Gemara rejects this proof from the verse, it brings another verse to support the opinion that a treifa can survive: "Between the living thing that may be eaten and the living thing that may not be eaten."

The Mishna's list does not include all cases, as there are additional cases of treifot—four that are referenced by the acronym BSGR, and another seven Amoraic traditions known as the "shev (seven) shematata." Although these cases are not explicitly mentioned in the Mishna, they can be derived from the rule stated at its end, according to which any animal that is incapable of living is considered a treifa. However, how can the tannaitic tradition of the school of Rabbi Yishmael, which limits the list of treifot to exactly eighteen, be reconciled? After a failed attempt, the Gemara settles the count according to Rabbi Yishmael by grouping all types of perforations into one broad category and all types of severed parts into another single category, thereby reconciling the calculated total with all the treifot appearing in the various lists.