Chullin, Chapter 9, Mishnah 1. This chapter turns to the laws of tumah as they relate to a slaughtered animal and its various parts. The opening mishnah asks which parts of the animal are treated as food, and it draws a sharp distinction between two different systems of tumah: the tumah of foods and the tumah of neveilah.
Let us begin with the background. Imagine a piece of food that became tameh, say it came into contact with a sheretz. That food is now tameh. But for it to pass its tumah along to another food that it touches, it must have a certain minimum volume: the volume of a kabeitzah, an egg. Anything less than that does not transmit.
Here the mishnah teaches something striking. That kabeitzah does not have to be composed entirely of genuine food. Certain items that are not really food in their own right can join together with actual food to make up the required volume, and once the measure is reached, the tameh food can transmit its tumah onward.
The list of parts that combine
The mishnah enumerates them one by one. "Ha'or veharotev": the hide of the animal that was slaughtered, together with the gravy, meaning a sort of liquid that thickens as it comes off the skin. "Vehakipah": the seasonings and spices that were mixed into the dish. "Veha'alal": those thin scraps of flesh that stay stuck to the hide once it has been peeled away from the carcass. "Veha'atzamot": bones, and more exactly bones that hold marrow. "Vehagidin": sinews, which nobody eats by themselves. "Vehakarnayim vehatelafim": hooves and horns, and here the intent is only their soft parts, the portions still tender enough to bleed were a knife taken to them.
Of every item on this list the mishnah declares "mitztarfin letamei tumat ochalin." Together with the flesh they help make up the volume of an egg, and once that quantity is present, food that is tameh can pass its tumah on to whatever food it touches.
What thread runs through the entire list? Each of these is something like a partial food. Some are "ne'echal al yedei hadachak": a person will eat them when circumstances press him, yet they would never be set on a table as a dish in their own right. Others, the hide, the bones, the horns and the hooves, act as a covering that guards the food rather than as food. Hence the two halves of the ruling: standing alone, none of them passes tumah to other foods even after becoming tameh, and yet, attached to genuine flesh, they help bring the quantity up to a kabeitzah, and at that point the tumah does move onward.
But not for the tumah of neveilah
"Aval lo tumat neveilot." For neveilah tumah the reckoning is different: not one of these items is counted along with the flesh. Even if they belong to the carcass itself, the capacity to transmit neveilah tumah rests with the meat alone. Every one of these accompanying parts, joined to the flesh yet not flesh, contributes nothing whatsoever to the measure.
A second case with the same pattern
A second illustration follows, again showing food tumah to be the more far-reaching of the two systems: "Kayotzei bo, hashocheit behemah temeiah lenochri umefarkeset." Someone performs shechitah on a non-kosher animal for a gentile; the throat has been cut, and the creature is still jerking and shuddering through its final moments before it lies still.
While it remains in that condition the mishnah says "metam'ah tumat ochalin": food tumah it already transmits. But "aval lo tumat neveilot ad shetamut": neveilah tumah waits until the twitching has ceased and death is complete, "o ad sheyatiz et roshah," that is, unless the head has been struck clean off.
Notice the pattern once again. With regard to the tumah of foods we are stringent, and the transmission takes effect even while the animal is still moving. With regard to the tumah of neveilah, nothing takes effect until the movement stops and the animal has died, or until the head has been removed.
The mishnah states the rule that emerges: "ribah letamei tumat ochalin mima sheribah letamei tumat neveilot." Both halachot, the flesh that adds up with its ancillary parts and the beast still in its death throes, point toward one conclusion: the Torah granted a broader set of cases the power to transmit food tumah than it granted the power to transmit neveilah tumah. Food tumah simply has more routes by which to travel.
Rabbi Yehudah on the shreds of meat
The mishnah returns to the small shreds of meat clinging to the hide and develops the point. "Rabbi Yehudah omer: ha'alal hamechunas." Rabbi Yehudah speaks of shreds of meat attached to a neveilah that a person went and gathered together. By collecting them and taking hold of them, he has turned them into a davar chashuv, something of significance. They are no longer nullified to the hide; they now carry the standing of food.
And so: "im yesh bo kezayit bemakom echad, chayav alav." Should the heap he assembled hold, in a single spot, a kezayit's worth of flesh, neveilah tumah is transmitted by it and liability attaches. Whoever touches it becomes tameh, and were he afterward to walk into the Beit Hamikdash or eat from a korban, he would be in transgression.