Zevachim Chapter 6, Mishnah 6. This mishnah comes to summarize what we learned previously regarding the bird chatas and the bird olah. Its fundamental point is that even though there are things that can go wrong and invalidate the offering, nevertheless, once the blood is properly placed on the wall of the Altar - in bird offerings just as in animal offerings - the remaining procedures, even if not done properly, do not invalidate the offering.
"Lo hesir es hamurah velo es hanotzah velo es bnei me'ayim hayotzim imah" - if he did not remove the crop, nor the feathers, nor the intestines that come out with it:
This refers to someone who brought a bird olah and did not remove the following parts from it:
"Hamurah" - the crop, as we mentioned.
"Hanotzah" - the feathers on the breast, which he must cut and remove with the small knife.
"Bnei me'ayim hayotzim imah" - the rest of the parts, the digestive system, and the gizzard that comes with it.
He must remove all of these before he places the bird on the fire, and if he did not do so - there is seemingly an invalidation here.
"Velo sofgo bamelach" - and he did not rub it with salt:
This refers to someone who failed in salting the offering. We said that the neck from the head is also salted, and the body after being halved is supposed to be salted as well. Here too, the matter is not as it should be.
"Kol sheshinah bah me'achar shemitzoh es damah, kesherah" - any deviation that he made in it after he squeezed out its blood, it remains valid:
Any of these deviations from the proper procedure that occur after the squeezing of the blood - and in the case of a chatas this refers to the squeezing out of the blood as well as the sprinkling - does not invalidate it. For once the blood reaches the Altar, and the squeezing is the main element, and since it was done properly - the offering is valid. If something was done improperly afterward, it could be a Torah prohibition or a failure to perform the mitzvah properly, but it does not invalidate the offering: the offering still accomplishes what it is supposed to accomplish.
"Hivdil bachatas velo hivdil ba'olah" - if he severed it in a chatas, or did not sever it in an olah:
In a chatas - if he completely separated the head from the body; and in an olah - if he did not separate the head from the body, and according to the Rambam, or if at the very least he did not cut the two signs, the windpipe and the esophagus - this is invalid and the offering is invalidated. The reason is simple: these actions are done before the receiving of the blood, which is squeezed from that neck onto the wall of the Altar.
"Mitzoh dam harosh velo mitzoh dam haguf" - if he squeezed the blood of the head but did not squeeze the blood of the body:
We are dealing here with the bird burnt-offering, which involves two squeezings of blood: first, he squeezes the head at the neck, and afterward the body. If he did only the head and not the body - it is invalid, and the offering is not acceptable, since the main part is the body.
In contrast, "Mitzah dam haguf velo mitzah dam harosh - kesherah" - if he squeezed the blood of the body but did not squeeze the blood of the head, it is valid: if he squeezed the blood from the body and did not manage to squeeze it from the head - the offering is valid. The reason is that the requirement is to extract the majority of the blood, and most of the blood is found in the body and not in the head. Therefore, even though omitting the head is a failure to perform the procedure properly, ultimately the offering is valid for that burnt-offering.