This Mishnah discusses blemishes in an animal’s reproductive organs. If any part of the area visible on the underside of the animal’s body, where the testicles are being held, is missing and will not grow back, or if any part of the private parts of a female animal is missing and will not grow back, the animal is disqualified, just like all other types of sacred offerings, male and female. If they are missing this part of their body, they would be disqualified.
If part of the bones of the tail is missing, it will not grow back. But not if the missing part is soft tissue in the joint between the vertebrae, which will grow back. Or if the skin at the tip of the tail is peeled off, exposing the bone. Or if there is flesh between the vertebrae that is one finger wide. In all these cases, the Bechor (firstborn) is disqualified.
Here, all the three possible blemishes that could be on the tail of the animal...