Zevachim, Chapter 6, Mishnah 2. The mishnah here turns to the main topic of the chapter - bird offerings: the bird sin-offering and the bird burnt-offering. These birds are brought together, two turtledoves (the turtledove is a type of wild dove) or two young pigeons (dove chicks), and usually the pair is divided so that one bird is a sin-offering and one bird is a burnt-offering.
Why does a person bring a bird sin-offering?
The main reason is the obligation of an adjustable offering. As stated in Vayikra 5, a person who entered the Beis Hamikdash in a state of tumah or who ate chelev in a state of tumah is obligated to bring a sin-offering; however, if he cannot afford it, it is an adjustable offering, and he can bring a pair of birds in its place - one for a bird sin-offering and one for a bird burnt-offering. And if he cannot afford even this, he brings a meal-offering - a sinner's meal-offering. An important point: since the Torah connects these two offerings, we learn certain halachos that apply to the bird sin-offering from the laws of that sinner's meal-offering.
A more common case is a woman after childbirth: if she cannot afford to bring a sheep, she brings a bird for a sin-offering as part of her purification process. There are also the zav, the zavah, the nazir, and the metzora, all of whom may bring these bird offerings according to their obligation. These are the reasons for bringing the bird offering.
"Chatas ha'of keitzad hayisah na'asis? Hayisah na'asis al keren deromis ma'aravis" - How was the bird sin-offering performed? It was performed at the southwestern corner:
The sacrificial action was performed at the southwestern corner of the altar, and all the service was concentrated there, as the mishnah will explain further.
There are three services in the bird sin-offering:
Melikah - killing the bird, which is done with the thumbnail from the back of the neck, unlike shechitah with a knife from the front (and we will elaborate on this further in the chapter).
Hazaah - sprinkling the blood on the altar at the southwestern corner.
Mitzui - squeezing out the remaining blood, also at the southwestern corner, above the base.
This needs to be understood: according to halachah, the melikah can be performed anywhere in the courtyard. However, since there is not much blood in a bird and one must act quickly, they would stand near the southwestern corner for reasons of order and logic, for that is where the hazaah and mitzui must be done. Therefore, the mishnah says that "anywhere, it is valid", "ela zeh hayah hamakom" - but this was the place established for it initially.
The source for this is the connection between the bird offering and the sinner's meal-offering: just as before the kemitzah, taking that portion from the meal-offering, one must perform hagashah - touching the vessel holding the meal-offering, the flour and the fine flour, to the southwestern corner of the altar, and this is the halachah initially - so too with a bird, the hazaah and mitzui are performed at the southwestern corner.
"Sheloshah devarim hayisah osah keren meshameshes milematah usheloshah milemalan" - That corner served three functions below and three above:
That same southwestern corner served three functions below, meaning below the chut hasikra (the red line dividing the altar), and an additional three functions above the chut hasikra.
Three from below:
Chatas ha'of - as described above.
Hagashos - bringing the minchah to the mizbeach, which is required before the kemitzah, is done by pressing it against the southwestern corner.
Sheyarei hadam - the remaining blood from all the korbanos is poured into small holes in the yesod. As we learned in Eizehu Mekoman, the blood of all korbanos is poured at the southwestern corner into the southern hole; whereas for the five korbanos burned outside the Beis Hamikdash, whose blood is sprinkled on the inner mizbeach, the blood goes into the western hole. There were two holes at this corner: one on the western side and one on the southern side.
Three from above:
Nisuch hamayim - on Sukkos there is a special concept of "and you shall draw water with joy", drawing the water and pouring it, from which comes the special Simchas Beis Hasho'eivah. The water is poured into a special bowl, like a basin, at the top of the mizbeach on the southwestern corner.
Nisuch hayayin - every olah and every shelamim, which constitute the majority of korbanos, are accompanied by nesachim that include a minchah and the pouring of wine. The wine is poured into the second bowl at the top of the mizbeach on that same corner. The water and wine flow down from the mizbeach into the shittin - a very deep cavity under the mizbeach where they collect. There is a discussion about how frequently they would clean it out, but from time to time it was necessary, because the wine would congeal down below in the shittin.
Olas ha'of - its offering is also performed there.
Let this not be confusing: the subject of our Mishnah is the chatas ha'of and not the olas ha'of. Indeed, the usual place for performing the olas ha'of is at the southeastern corner. The reason, as we will see, is that its crop, digestive tract, and feathers must be removed, and all of these are thrown onto the floor in a special place - the makom hadeshen, where the kodashim and the ashes, as well as the remains of the cleaning of the menorah, are placed. This place is located on the eastern side of the kevesh, ten amos inward from the south, and since the parts of the bird go there, the one performing the avodah for the olas ha'of must stand at the southeastern corner. However, sometimes the area is too crowded, and when it is not possible to do it there, they are permitted to go up to the southwestern corner on top of the mizbeach. The reason they can go up there is that the blood of the olas ha'of must be placed above the red line anyway, and therefore it is a suitable location.
In summary: The chatas ha'of is performed at the southwestern corner from below, with three avodos - melikah, hazayah, and mitzuy - while the olas ha'of is performed from above. It is worth repeating and emphasizing a counterintuitive point: for an animal korban - the blood of the chatas goes above and the blood of the olah goes below; whereas for bird korbanos - the blood of the olah goes above and the blood of the chatas goes below.