פירוש על זבחים 9:4

כשם שאם עלו לא ירדו – all of these are invalid as it is taught in the Mishnah regarding them that they should not go down.

Just as they do not descend once they have ascended, so they do not ascend if they have descended. Once one of the disqualified sacrifices listed in mishnah two is taken off the altar, it cannot be put back on.

And all of these, if they ascended alive to the top of the altar, they must descend. In contrast, if a live animal is put on the altar it may be taken off. The altar only sanctifies sacrifices that have already been slaughtered.

וכולם שעלו חיים בראש המזבח (see Mishnah 2 of this chapter) – Rabbi Akiva stated this that he declares valid in the case of animals that are blemished. And he agrees that if they went up while living on the top of the altar, they should come down, for the altar does not sanctify animals with a blemish while living.

An olah which ascended live to the top of the altar, it must descend. If an olah is put alive on the altar, it still should be taken off. It should not be slaughtered there, even though all of it will eventually be burned on the altar.

עולה שעלתה חיה לראש המזבח תרד – we are speaking of a kosher burnt-offering, and it is the words of all. But the Mishnah did not take this usage other than because of the concluding clause [of the Mishnah], to teach you that the top of the altar ןדan appropriate place for flaying it and dissecting/dividing it where he transgressed and slaughtered it at the top of the altar.

If one slaughtered it on the top of the altar, he must skin it and dismember it where it lies. If, however, one did slaughter the olah on top of the altar, it has now become sanctified and cannot be taken down. It should be skinned and dismembered there on the altar. Then the skin can be removed for burning elsewhere and the pieces can be burned right there on the altar.