It means that the priest does not have to separate it, but not that it is prohibited to do so. Rav Aḥa, son of Rava, said to Rav Ashi: If that is so, then with regard to a pit in the public domain, where it is written: “And if a man shall open a pit…and does not cover it” (Exodus 21:33), can one claim that this verse also means that he does not have to cover it?

The Gemara responds: How can these cases be compared? There, with regard to a pit, since it is written in the following verse: “The owner of the pit shall pay” (Exodus 21:34), it is evident that it is incumbent upon him to cover the pit. But here, since it is written with regard to a bird burnt offering: “And the priest shall bring it to the altar” (Leviticus 1:15), the term “it” indicates that the verse is referring only to a burnt offering, and the verse has thereby differentiated between a bird sin offering and a bird burnt offering.

Consequently, it is obvious that whereas the priest must completely separate the head of a bird burnt offering, this is not the halakha with regard to a sin offering. Why do I need the verse to state with regard to a bird sin offering: “But shall not separate it” (Leviticus 5:8)? Conclude from this verse that it is not forbidden to separate the head of a bird sin offering from the body, but rather one does not have to separate it.

§ The mishna teaches that if the priest squeezed out the blood of the head and did not squeeze out the blood of the body, it is disqualified. If he squeezed out the blood of the body and did not squeeze out the blood of the head, the offering is valid. The Sages taught in a baraita: In reference to a bird burnt offering, the verse states, seemingly unnecessarily: “It is a burnt offering” (Leviticus 1:17). This teaches that even though the priest squeezed out the blood of the body and did not squeeze out the blood of the head, it is valid. One might have thought that if the priest squeezed out the blood of the head and did not squeeze out the blood of the body the offering is still valid. Therefore, the verse states: “It is.”

The Gemara asks: What is the biblical derivation for the opinion that the offering is valid if the priest squeezed out only the blood of the body but not if he squeezed out only the blood of the head? Ravina said: There is no conclusive proof from the language of the verse itself, but it stands to reason that this is the case, as most of the blood is found in the body, not the head.

MISHNA: If the priest sacrificed a bird sin offering in its designated place below the red line, and he sacrificed it according to the procedure of a sin offering with pinching, i.e., cutting from the nape with a fingernail, and sprinkling, and he sacrificed it for the sake of a sin offering, the offering is fit. This is the manner in which a priest is to sacrifice a sin offering ab initio.

If the priest sacrificed the bird sin offering below the red line in the middle of the altar and according to the procedure of a sin offering, but he sacrificed it for the sake of a burnt offering; or if he sacrificed it according to the procedure of a burnt offering, even if he sacrificed it for the sake of a sin offering; or if he sacrificed it according to the procedure of a burnt offering for the sake of a burnt offering; in all these cases the sin offering is disqualified. If one sacrificed a bird sin offering above the red line according to the procedure of any of the offerings, it is disqualified, because he did not sacrifice it in its designated place.

A bird burnt offering that one sacrificed in its designated place above the red line according to the procedure of a burnt offering and for the sake of a burnt offering is fit. This is the manner in which a priest is to sacrifice a burnt offering ab initio. If he sacrificed a bird burnt offering above the red line according to the procedure of the burnt offering but for the sake of a sin offering, the offering is fit, but it did not satisfy the obligation of its owner.

If the priest sacrificed a bird burnt offering according to the procedure of a sin offering for the sake of a burnt offering, or according to the procedure of a sin offering for the sake of a sin offering, the offering is disqualified. If he sacrificed it below the red line according to the procedure of any of the offerings, it is disqualified, because he did not sacrifice it in its designated place.