The Mishnah reported a Machlokes regarding the replacement Se'irim discussed by R. Meir and R. Elazar/R. Shimon above.

(R. Meir): Only the last Sa'ir is deal with as the actual one (it is burnt and those who deal with the burning contract Tum'as Begadim).

(R. Elazar and R. Shimon): All of them must be dealt with in the same way.

Question: In light of the above, how Many Se'irim are sent out as the Mishtale'ach?

Answer: Shall we send out his whole flock (surely, only one)!

Question: But he could have his whole flock burned (multiple Se'irim Lashem)!?

Answer: There is no comparison since the Sa'ir ha'Mishtale'ach is restricted by "Oso".

It is a Machlokes regarding the opinion of Rava whether to send out the first Sa'ir (R. Papi) or the last (R. Simi).

Question: Why the first (the second makes sense since the Kaparah was completed with its pair)?

Answer: R. Papi holds like R. Yosi who holds that the Mitzvah is to be performed with the first animal so designated.

Question: Where is this opinion of R. Yosi?

Answer: When R. Yosi explains the requirement to mark the Kupos as in order to use the first one first.

Question: But that may be required since the second has not yet become usable when the first Kupah was available, but here all the Se'irim become available at the same moment (conclusion of the Matnos Damim)!?

Answer: Rather, the source is R. Yosi regarding the Korban Pesach which was lost, replaced and then found where R. Yosi holds that the first is to be used.

The two Se'irim must be the same in appearance, height, price, and time of purchase.

This requirement, however, is not Me'akev (an example of an imperfect, but Kosher, pair would be if one Sa'ir died before the Goralos, a pair may be brought for the remaining Sa'ir).

If one died after the Hagralah, a new pair is brought and a Hagralah is used to determine the replacement for the one which died.

The second Sa'ir pastures until it develops a blemish (since a Korban Tzibur is not put to death).

(R. Yehudah): The extra Sa'ir is put to death.

R. Yehudah further teaches that if the Dam Sa'ir la'Shem was prematurely spilled out (such that another Sa'ir is slaughtered) then its corresponding Sa'ir ha'Mishtale'ach is put to death; similarly if the Sa'ir ha'Mishtale'ach dies, the blood of its counterpart is spilled out.

The Beraisa draws from the word "Sh'nei" that the Se'irim must be alike.

Question: How do we know that their similarity is not Me'akev?

Answer: From the repetition of the (singular) word Sa'ir.

Question: Whence would we have thought that it was Me'akev?!

Answer: The multiple repetition of "Sh'nei" might lead us to consider their being identical as Me'akev.

Question: Then, now, what is the role of the three-fold repetition of "Sh'nei"?

Answer: One for appearance, one for height, and one for value.

The same sequence appears in the Beraisa regarding the two Kivsei Metzora, and in the Beraisa regarding the Tziporei Metzora.

Question: If "Sh'nei" and "Sh'tei" teach the requirement of alike pairs, then the word "Shenayim" by the Temidim should teach the same Din there (as the sequence would work there)?

Answer: The word "Shenayim" by Tamid is not extra; it is needed to teach that they must be slaughtered in the sunlight, not in the shade.

The Beraisa goes on to demonstrate that the number here cannot be teaching the obvious number since the Pasuk is explicit regarding "the one... " and "the one... ".

Question: Where in the Azarah would the sunlit Shechitah take place?

Answer: The Tamid in the morning is slaughtered in the NW corner (angled back into the SE sun, using the second row of rings) and the afternoon Tamid is in the NE (angled back to the setting sun in the SW).

The Musafim of Shabbos should (according to Rashi) be alike.

One is Chayav for Shechutei Chutz for slaughtering either Sa'ir prior to the Hagralah.

After the Hagralah one is Chayav only for the Sa'ir la'Shem.

Question: Prior to the Hagralah neither animal is fit for a Korban, so why is there a Chiyuv on them?

Answer: Since (Ho'il) they are fit to be the Chatas ha'Musafin (brought on the Mizbe'ach ha'Chitzon), they are deemed fit.

Question: But the Avodas ha'Yom needs to be completed before such a Sa'ir Musafin could be fit to be brought!?

Answer: Timing alone does not render an animal unfit if its time will come that day.

With this lesson from R. Chisda (that missing an action, such as Hagralah, renders an animal unfit) we can understand the Din of R. Yehudah citing Shmuel:

A Shelamim is Pasul if slaughtered before the gates of the Heichal are opened.

By extension, the Chiyuv of Shechutei Chutz will not apply to that animal since opening the gates is like an action which stands between the animal and its fitness to be offered.