Gemara

42b (Mishnah - Beis Hillel): A spine missing even one vertebrae is incomplete (it does not have Tum'as Ohel);

(Rav Yehudah): The same amount missing makes an animal Tereifah.

43a (Beraisa - R. Yosi b'Rebbi Yehudah): If the gall bladder was punctured, it is Tereifah.

Chachamim: Iyov said "my gall bladder spills to the ground", yet he lived!

R. Yosi: We cannot learn from miraculous cases. Iyov's kidneys were stricken. According to nature, he could not survive. He was kept alive miraculously - "just guard his soul (that he will not die)."

56b (Mishnah): If the intestines came out (and were returned), and they were not punctured, this does not make a bird Tereifah.

(R. Shmuel bar R. Yitzchak): This is only if they were returned the same way. If they were reversed, it is Tereifah.

A man fell, his stomach split, and his intestines came out. A Nochri made him feel great anguish; his intestines recoiled into his body without reversing, and the Nochri sewed him up (and he lived.)

57b (Beraisa): If there is a long hole in the skull, or many small holes that add up to the area of a drill (it is Tereifah);

R. Yosi ben ha'Meshulam says, a case occurred in which a man's skull was pierced. They covered over it with a gourd, and he lived.

R. Shimon ben Elazar: This does not prove (that this is not a Tereifah). He was hurt in summer, and he died that winter!

Bava Kama 51a - Question (Mishnah): The scaffold for people sentenced to stoning was twice a person's height. (They were pushed off the scaffold, and stoned if they did not die from the fall.)

If a fall less than 10 Tefachim can kill, why did the scaffold need to be so high?

Question: A Beraisa obligates a Ma'akah (wall) around a roof only if the house is at least 10 Tefachim above street level. If a fall even less than 10 Tefachim can kill, even a lower house should require a Ma'akah!

Gitin 56b: A mosquito entered Titus' nose and bored into his brain for seven years.

(Beraisa - R. Pinchas ben Arova): When he died, they pierced his skull. A wild bird was found, weighing two Sela'im.

(Abaye): Its mouth was copper, and its claws were iron.

Rishonim

Tosfos (42b DH v'Omar): Rav Yehudah learned from the Seifa of the Mishnah, regarding a hole in the skull, that this is a Tereifah. Why didn't the Gemara ask we should include a hole in the skull in the list of Tereifos? R. Tam says that this is only if also the membrane is punctured, and in an animal, a hole in just the membrane is a Tereifah. Man has Mazel, so he is Tereifah only if also the skull was punctured. However, the Gemara assumes that what is not Tereifah in a man (Iyov) is not Tereifah in an animal! Seemingly, a hole in just the skull is Tereifah, for it will cause the membrane (aound the brain) to (eventually) be punctured. However, we cannot say so, for many people live with a hole (the size that makes a Tereifah) in the skull for many years. Rather, a hole in the skull together with a hole in the outer membrane is Tereifah, for then the inner membrane will (eventually) be punctured. Some say that in an animal, the inner membrane suffices (if it is intact). Even the opinion that a hole in the outer membrane itself is Tereifah in an animal, can say that animals are different, but unlike R. Tam. Rather, the inner membrane in man is hard, so he is Tereifah only if the skull and outer membrane were punctured, but the inner membrane in animals is soft, so a hole in the outer membrane itself makes a Tereifah. However, we distinguish people from animals only when there is such a reason.

Chasam Sofer (52): We must say that man is different, at least regarding the knee. The Rashba (Chulin 54b DH Gufa) says that birds fly and do not lean on the thigh so much, so a detached thigh does not cause it as much pain as it does to an animal, therefore, this is not a Tereifah in birds. All the more so it is not a Tereifah in man, for he can sit or lie and not move his leg at all!

Tosfos (Bava Kama 51a DH Na'avid): Our Gemara equates Tereifos of people to those of animals, like Chulin 43a. This is difficult for R. Tam.

Tosfos (Gitin 56b DH v'Niker): Titus did not become a Tereifah, for the mosquito entered through his nose and did not pierce the membrane of the brain. Also, we can distinguish between Tereifos of man and of animals.

Tosfos (Chulin 43a DH Yiflach): Rashi says that Iyov's kidneys were stricken in a way that makes them Tereifah. What was the source to assume so and ask how he lived? Rather, whenever the kidneys are stricken one cannot live without a cure, and we do not see that Iyov received a cure.

Poskim

Shulchan Aruch (YD 31:1): If only the outer membrane of the brain was punctured, it is Kosher.

Rema: Some say that it is Tereifah.

Shulchan Aruch (3): If a worm was found in the membrane, but the brain is intact, and there is no mark or blood in the membrane, it is Kosher. Some say that we do not know how to check for this, so it is Tereifah.

Gra (8): One answer in Tosfos Gitin 56b distinguishes Tereifos of people from Tereifos of animals, like R. Tam. Tosfos in Zevachim refuted this from Chulin 43a. Also Chulin 57b refutes this.

Pri Chodosh (7): Piskei Tosfos (Zevachim 79) says that Tereifos of man live longer than Tereifos of animals. This does not mean that they live more than 12 months, for this is unlike the Rambam, and the Magid Mishneh, Ramban and Rashba from the Yerushalmi. Also Tosfos (Avodah Zarah 6a DH v'Dilma) says so. We can learn also from Tosfos Chulin (11b DH v'Dilma), Chulin 43a, 56b, and 57b. Tosfos says in the name of R. Tam that man's Mazel enables him to live more, i.e. some Tereifos of animals are not Tereifah in people, but surely a Tereifah person cannot live more than 12 months. The Kesef Mishneh misunderstood. According to Tosfos, R. Tam has no proof. Tosfos is correct. The sources I brought prove that Tereifos of animals are also Tereifah in people, wherever man and animals are the same (but not when they differ biologically, e.g. man's membrane is harder).

Pri Megadim (Sifsei Da'as 1): We cannot learn from animals, for man's membranes are harder. It seems that we do not distinguish Tereifos in people from Tereifos of animals. Also a Tereifah person cannot live more than 12 months. According to the Yam Shel Shlomo, 12 months should not permit a widow to remarry, for there is a Chazakah of Eshes Ish, and a minority who live more than 12 months. Mid'Rabanan, this is like an even Safek! We must say that the Mishnah permitted because water worsens the wound, or because Chachamim knew that for this Tereifah, no one will ever live more than 12 months.

Pleisi (5): The lenient opinion learns from Titus. How can we learn from the supernatural? I answer that Hash-m would do miracles to punish him, but not for his benefit, to live more than a year if he were Tereifah. We should be stringent like R. Tam, and not learn from here to permit animals. However, we should learn that a man is Kosher even if both membranes were punctured! We must say that a human Tereifah can live more than 12 months. Titus was from the minority, who live more than 12 months. R. Yosi tried to bring a proof about a hole in the skull, for it is more lethal and kills within 12 months. There is no question against R. Tam from Iyov. Mazel merely helps that there are times when man can be cured; in Shabbos (53b), we say that amulets help only for people. We do not find that Iyov received a cure.