Chullin, Chapter 6, Mishnah 7. This chapter is devoted to kisuy hadam, the mitzvah of covering the blood of a slaughtered wild animal or bird. Until now the chapter has dealt with when the obligation applies and who is bound by it. Here the Mishnah turns to the material itself: with what substance is the blood actually covered?
The starting point is the wording of the Torah, which speaks of covering the blood with afar, dirt or earth. One might have assumed that earth alone qualifies. The Mishnah teaches otherwise: afar is not an exclusive requirement but an illustration, and a range of other substances share its relevant qualities and are therefore acceptable.
The Mishnah's Question
The Mishnah opens: "bameh mechasin uvameh ein mechasin?" With what do we cover the blood, and with what do we not cover it?
The Permitted Materials
"Mechasin bezevel hadak uvchol hadak": one covers with fine manure and with fine sand. Both resemble earth in two respects. They are capable of sustaining the growth of plants, and they are fine and granular, so that the blood can mingle with them and be absorbed.
"Besid uvcharsit": with lime and with crushed pottery. These too are fit for kisuy hadam.
"Uvilveinah uvimgufa sheketashan": with an earthenware brick or the stopper of a barrel, provided they have already been ground up. Once they have been broken down into fine particles, they may serve for the mitzvah.
The Disqualified Materials
Now the mishnah turns to what is unfit: "aval ein mechasin", but we do not cover the blood. Ruled out is "zevel hagas", manure that is coarse, and equally "chol hagas", coarse sand. What disqualifies them is precisely their coarseness: being thick and lumpy, they bear no resemblance to fine earth at all.
"Velo vilveinah uvimgufa shelo ketashan": nor with an earthenware brick or a barrel stopper that have not been ground up. In their whole state they cannot absorb the blood.
A further exclusion follows: "velo yichpeh alav", one may not turn anything over upon the blood, and specifically "et hakeli", a vessel. It makes no difference what material the vessel is made from. Setting it mouth downward over the blood removes it from sight, yet mere concealment is not the act of covering that the Torah asks for.
Rabban Shimon ben Gamliel's General Rule
The mishnah concludes with a summarizing principle. "Klal amar", a general rule was stated, and its author was "Rabban Shimon ben Gamliel". His formulation runs as follows. "Davar shemegadel bo tzmachim", anything in which vegetation is able to take root, "mechasin bo", is valid for the covering. The converse holds as well: "veshe'eino megadel tzmachim", a substance in which nothing will grow, "ein mechasin bo", may not be used at all.
A single idea unifies every item on both lists: does the substance stand comparable to the afar named in the pasuk? Earth has two defining characteristics. Seeds take root in it, and its texture is powdery rather than lumpy. Whatever possesses both traits functions as a substitute for earth, and the blood may properly be covered with it.