Taharos, Chapter 9, Mishnah 8. This chapter follows olives through the stages of their production, from the moment they are picked until the oil is pressed out, and asks at each stage whether they are already susceptible to tumah and how tumah spreads through them. Our Mishnah returns to the press itself and to a very practical problem: a dead sheretz turns up somewhere in the works. How far does its tumah reach?
Found among the crushed olives
"Hasheretz nimtza berechayim": the sheretz turned up among the heavy grinding stones that crush the olives before they go to the press. The Mishnah rules "ein tamei ela mekom maga'o": only the precise point of contact becomes tamei, and nothing beyond it.
One would have expected otherwise. Since the olives are all lying together in the mill, we might assume that the piece the sheretz touched passes its tumah on to the piece beside it, and so on through the whole batch. That is not so. Food conveys tumah to other food only when it has the volume of a kabeitzah. A whole olive is already smaller than a kabeitzah, so a crushed fragment of an olive is certainly smaller. Each fragment is therefore too small to hand tumah on to its neighbor, and the damage stops exactly where the sheretz lay.
When liquid is running
"Im hayah mashkeh mehalech, hakol tamei": if liquid was flowing among the olives, everything is tamei. Liquid changes the picture entirely. It carries the tumah from place to place, and unlike the small olive fragments it renews its status as a rishon each time it receives tumah and passes it along. Once there is running liquid connecting the olives, the whole batch is affected.
Found on the leaves
"Nimtza al gabei ha'alim": the carcass was discovered resting upon the foliage. Since foliage is not food and no one eats it, it cannot receive tumah in the first place, and a sheretz sitting there has conveyed nothing to it. All that remains to clarify is whether the sheretz brushed against the olives on its way to that spot.
For that the Mishnah supplies a procedure: "yish'alu habaddim lomar lo naganu." Those laboring in the press are asked, and they respond that no contact took place. Now, these workers are amei ha'aretz who have been purified so that they may handle the olives; the taharah they undergo does not elevate them to the standing of chaverim, and they retain their status as amei ha'aretz. Even so, their word is accepted here, and once they say the sheretz never reached the olives, we treat it as having touched only the foliage.
Touching the heap
"Im hayah noge'a bahem afilu bese'arah": if the sheretz was in contact with the olives, even by a single hair, the entire pile is tamei. A heap of olives is not treated as a collection of separate items, each too small to transmit tumah. It is regarded as one single unit, so the slightest point of contact anywhere on the heap renders all of it tamei.
The two halves of this Mishnah thus balance one another. Crushed fragments scattered in the mill are individuals, and tumah touches only what it physically reaches. A heap, however, is a single body, and the faintest touch makes the whole of it tamei.