We are in Maseches Menachos, chapter 7, mishnah 7. Our mishnah refers back to the three offerings mentioned in the previous mishnah as requiring tenufah (waving), and it teaches an interesting principle: there are three mitzvos that apply to these three offerings, but in each one of them only two of the three are fulfilled, while the third mitzvah drops away and does not apply to it.
The three offerings:
Shelamim of an individual - the peace offering brought by a private person.
Shelamim of the community - the communal peace offerings, which are none other than the lambs of Atzeres, the two lambs brought on Shavuos.
Asham of a metzora - the guilt offering brought by a metzora.
The three mitzvos:
Waving while alive - waving the animal while it is still living.
Waving after slaughter - waving the meat after the slaughter, both the portions offered on the mizbe'ach and those given to the kohanim.
Semichah - placing the hands on the head of the animal and pressing down on it before the slaughter.
The rule in the laws of semichah:
The general rule is that offerings of an individual require semichah, while communal offerings do not require semichah. There are exceptions to this rule, and although they do not bear directly on our mishnah, they are worth knowing:
The lighter offerings of an individual - the bechor, the ma'aser and the pesach - those offerings that require only a single application of blood, do not require semichah before the slaughter.
Two communal offerings that do require semichah: the sa'ir hamishtale'ach on Yom Kippur, which is sent to the wilderness and pushed off the cliff, upon which the hands are placed and the confession is recited; and also the par he'elem davar of the community - when the Sanhedrin ruled mistakenly in a matter for which one is liable to bring an offering, and it turned out that the majority of the people followed them in error, and instead of the individuals bringing their own offerings the community brings a bull, and semichah is performed upon it.
The words of the mishnah:
Rabbi Shimon says: "Sheloshah minim te'unin shalosh mitzvos, shtayim b'chol achas v'achas, v'ein hashelishis bahen" - the three types of offerings listed in the previous mishnah require three mitzvos, and in each one of them only two apply, while the third does not apply to it.
"V'eilu hen: zivchei shalmei yachid, v'zivchei shalmei tzibbur, v'asham metzora" - these are the three offerings that the mishnah deals with, and this is how they divide up:
Shelamim of an individual - they require semichah while alive and waving after slaughter. As was explained earlier, one waves the eimurim that are offered on the mizbe'ach, and together with them the breast and the thigh, which are the gifts of the kehunah. The owner holds the portions and waves them, with the hand of the kohen beneath his hand; and if the owner is a woman, the kohen waves alone.
Shelamim of the community, which are the lambs of Atzeres brought on Shavuos - they require waving while alive and waving after slaughter, so that they are waved twice: first the two lambs are waved while still alive together with the shtei halechem, and afterwards they are treated according to the law of shelamim, and the eimurim are waved along with the breast and the thigh.
Asham of a metzora - it requires semichah and waving while alive. The metzora performs semichah on the asham, since an asham of an individual always requires semichah, and the verse teaches that before its slaughter the asham offering is waved together with the log of oil. But it has no waving after slaughter - once it has been slaughtered there is no waving of the eimurim.
In summary: In this Mishnah we learned that three offerings - the peace offering of an individual, the communal peace offering, and the guilt offering of a metzora - require three mitzvos altogether, while only two of them apply to each one: the individual's peace offering requires semichah while the animal is alive and tenufah after it is slaughtered; the communal peace offering requires tenufah while alive and tenufah after slaughter; and the guilt offering of a metzora requires semichah and tenufah while the animal is alive. We also saw the general rule that offerings of an individual require semichah while communal offerings are exempt from it, along with the exceptions on both sides.