Mishnah 9 in the ninth chapter of Maseches Menachos sums up the subject of semichah. Semichah really belongs to the topic of zevachim - animal offerings - and not to menachos, yet it is taught here nonetheless. The Mishnah compares the obligation of semichah in animal offerings with the obligation of tenufah, waving, which applies to various offerings.
The Mishnah presents two stringencies: one stringency that applies to semichah and not to tenufah, and a general stringency that applies to tenufah and not to semichah. In its words: "Chomer bisemichah bitenufah, uvitenufah bisemichah" - there is an aspect in which semichah is more stringent than tenufah, the waving of the offering, and there is an aspect in which tenufah is more stringent than semichah, the placing of the hands and pressing down on the head of the animal.
The stringency of semichah:
A person who pledges to bring an offering may bring it by himself, and he may also bring it in partnership with others. For example, twenty men who share together in the cost of a shelamim offering and bring it jointly on behalf of them all. In such a case each and every one of them must perform semichah himself, so that semichah is performed on that same animal twenty times, since every owner is obligated in semichah.
Tenufah, by contrast: in a shelamim offering the breast and the thigh are waved, with the kohen placing his hands beneath the hands of the owners, beneath the emurim and the breast and the thigh, and everything is waved in six directions. Even if a group of twenty men brings the offering in partnership, it is enough for one person to wave on behalf of them all, since the waving is done with the offering itself. This is not so with semichah, where every owner and every partner - in the language of the Mishnah, every member of the group - performs semichah separately.
These are the words of the Mishnah: "She'echad menif lechol hachoverim, ve'ein echad somech lechol hachoverim" - one person waves, wherever waving is required, on behalf of all the members of the group; whereas in semichah one person cannot perform semichah on behalf of the others, but rather each one performs it himself.
The version before us reads "choverim," and some have the reading "chaverim." "Chaverim" - the associates and partners; "choverim" - the members of the group. The idea is very similar.
The stringency of tenufah:
The stringency of tenufah lies in its broad scope: tenufah applies to many different types of offerings, whereas semichah applies only to the bringing of an animal offering - a zevach. This is not a sweeping rule, since not everything requires tenufah, but its range is far wider. This is how the Mishnah spells it out:
"Bekorbenos hayachid uvekorbenos hatzibur" - tenufah applies to communal offerings, such as the shtei halechem, and also to individual offerings; this is not so with semichah, for there is no semichah in communal offerings apart from the two exceptions discussed in the previous mishnayos. And there are further examples of this.
"Bechayim uvishechutin" - tenufah applies both to live animals and to slaughtered ones. So, for example, with the kivsei atzeres, the two lambs of Shavuos, which are waved while they are still alive and are waved again after they have been slaughtered. Semichah, however, is performed only on a live animal, before it is slaughtered.
"Bedavar sheyesh bo ruach chaim uvedavar she'ein bo ruach chaim" - tenufah applies equally to living creatures and to things that are not living, such as the shtei halechem, those loaves of bread that are waved and are not living creatures; whereas semichah applies only to a living animal.
It emerges, then, that "mah she'ein kein bisemichah" - all those applications of tenufah in the various types of cases do not apply to semichah at all, for semichah is performed only on a live animal brought as a zevach.