GEMARA: Shmuel says: In a case where the head of a fetus emerged and then went back into the womb, the offspring is not considered to have been born and does not exempt the next fetus from the obligation of redemption of the firstborn, e.g., if its twin brother was born first. Shmuel says this halakha specifically in a case of miscarriage, i.e., where the fetus whose head emerged was a stillborn and the one that was eventually born first is a viable offspring. But in a case where both are viable offspring, the emergence of the head is considered birth.

The Gemara asks: What is the reason for Shmuel’s ruling? The verse states: “All in whose nostrils was the breath of the spirit of life” (Genesis 7:22), from which it is derived: Anywhere that one has the breath of the spirit of life, i.e., if it is viable, one goes by its nostrils, i.e., its head is considered significant. But with regard to another offspring, one that is not viable, its head is not considered significant.

The Gemara raises a difficulty: We learned in the mishna: What is a firstborn with regard to inheritance but not with regard to redemption from a priest? It is a son who came after the miscarriage of an underdeveloped fetus, even where the head of the underdeveloped fetus emerged alive; and a fully developed nine-month-old fetus whose head emerged dead. Although the mishna addresses a nine-month-old fetus as well, in any event it teaches with regard to a miscarriage that its head exempts the offspring born after it. The Gemara responds: What is the meaning of the term: Its head? It means its head and most of the body.

The Gemara asks: But if so, let the mishna teach: Most of it. The Gemara answers: By right, the mishna should have taught: Most of it, but it did not do so, since in the latter clause of the mishna it needs to teach: A fully developed nine-month-old fetus whose head emerged dead. It is inferred from there that the reason the subsequent son is the firstborn with regard to inheritance is that the head of this fetus emerged dead, but if it was a nine-month-old fetus whose head emerged alive, then the fetus that comes after it is not a firstborn with regard to inheritance either. Therefore, the tanna of the mishna taught in the first clause also that the head of a miscarriage exempts the subsequent son, to maintain stylistic uniformity.

The Gemara asks: And according to this interpretation, what is the mishna teaching us? Is it that once the offspring reached out its head from the womb it is considered a birth? We learn this in a mishna with regard to the fetus of an animal (Ḥullin 68a): If a fetus reached out its head, although it returned the head, the halakhic status of that fetus is like that of a newborn, whose consumption is permitted only by its own slaughter.

And if you would say that the mishna there teaches us this halakha with regard to animals, and the mishna here teaches us that the same halakha applies to a human, this does not resolve the difficulty. The Gemara first explains why two rulings might be necessary with regard to people and animals: The reason is that the halakha of a human cannot be derived from that of an animal, as the animal has no concealed opening, i.e., the opening of an animal’s womb is not hidden. Consequently, one might have thought that only in the case of an animal is the emergence of the head considered a birth. By contrast, in humans, where the woman’s thighs conceal the opening of the womb and the emergence of the head alone is not noticeable, perhaps the emergence of the head is not considered a full-fledged birth.

Conversely, had this ruling been taught only with regard to humans, one would have said that the halakha of animals cannot be derived from that of a human because the countenance of a person’s face is significant, as people are created in the image of God. This is not so with regard to animals.

After clarifying why both rulings are necessary, the Gemara explains why this does not resolve the difficulty: We learn that ruling with regard to people also, in a mishna (Nidda 28a): If the fetus emerged in the usual manner, head first, it is considered born only when most of its head emerges. And what is considered most of its head? It is from when its forehead emerges. Accordingly, there was no need for the mishna here to state the halakha with regard to the head of a nine-month-old fetus, and the mention of a head with regard to a miscarriage contradicts the opinion of Shmuel. The Gemara comments: The refutation of the opinion of Shmuel is indeed a conclusive refutation.

§ Concerning this matter, Rabbi Shimon ben Lakish says: The emergence of a forehead alone in the case of a person exempts, i.e., is considered a birth, in all cases, except with regard to inheritance. If a son reached out his head alone and then brought it back, after which his twin brother was born, the second brother is the firstborn with regard to inheritance. What is the reason? The Merciful One states: “For he shall recognize the firstborn, the son of the hated, by giving him a double portion of all that he has” (Deuteronomy 21:17), and recognition is not attained by emergence of the forehead alone. And Rabbi Yoḥanan says: Even with regard to inheritance the emergence of a forehead is sufficient.

The Gemara asks: When Rabbi Shimon ben Lakish says the emergence of a forehead alone in the case of a person exempts in all cases, what does this comprehensive phrase serve to include? The Gemara answers that it serves to include that which the Sages taught: With regard to a female convert whose offspring reached out its forehead alone in her gentile state, and then she converted and gave birth to the entire child, one does not assign to her the days of ritual impurity and the days of ritual purity of a Jewish woman who gave birth. And likewise she does not bring the offering that a woman is obligated to sacrifice after giving birth, as the child is considered to have been born while the mother was still a gentile.

The Gemara raises an objection to the opinion of Rabbi Yoḥanan from a baraita: When the verse states: “He shall recognize” (Deuteronomy 21:17), this is referring to the recognition of the face. And what exactly is the recognition of the face? It is recognizing the countenance of the face with the nose. This indicates that the forehead alone is insufficient. The Gemara answers: Teach the baraita as saying: Up to, but not including, the nose. The Gemara suggests: Come and hear a mishna (Yevamot 120a): One can testify that a man died, in order to permit his wife to remarry, only if he can attest to seeing the countenance of the face with the nose, as this allows one to identify the individual definitively. Once again, the Gemara answers that one should teach: Up to, but not including, the nose.

The Gemara suggests: Come and hear another proof: If people saw the forehead of a dead person without the countenance of the face, or the countenance of the face without the forehead, they cannot testify that he died and render his wife permitted to remarry until they see both the countenance of the face and the forehead, with the nose. And Abaye says, and some say it was Rav Kahana who says: What is the verse from which it is derived? “The recognition of their countenance does witness against them” (Isaiah 3:9), and there is no recognition of a face without the nose. The Gemara answers: Testimony enabling a woman to remarry is different, as the Sages were stringent with regard to it. Therefore, they required greater proof than with regard to the halakhot of a firstborn.

The Gemara asks: And were the Sages stringent with regard to this testimony? But didn’t we learn in a mishna (Yevamot 122a): The Sages established that they would allow a woman to marry again based on testimony that is generally not accepted, such as testimony based on hearsay, i.e., the testimony of one man which was heard from another man who saw her husband die, from a woman’s testimony, from a Canaanite slave’s testimony, or from a Canaanite maidservant’s testimony? The Gemara answers that when the Sages were lenient it was with regard to the end of the testimony, i.e., to accept testimony that a husband had died even from individuals just mentioned. But the Sages were not lenient with regard to its beginning, i.e., the basic clarification of whether the witnesses properly identified the dead person when they saw him.

And if you wish, say instead that Rabbi Yoḥanan can resolve the difficulty as follows: