Tevul Yom, Chapter 2, Mishnah 4. This Mishnah continues the chapter's running theme: when a tevul yom touches one point of a mixture, how far does his touch reach? In other words, what is considered mechubar, joined together, so that touching a part is like touching the whole, and what remains a collection of separate items even when they sit together in one dish?
Porridge of terumah with chullin ingredients
"Hamikpah shel terumah, vehashum vehashemen shel chullin, shenaga tevul yom bemiktzasan, pasal es kulam." Picture a stiff porridge of terumah that has been seasoned with chullin garlic and chullin oil, and a tevul yom made contact with one part of it: the ruling is that he has rendered the entire dish unfit. Those seasonings have been absorbed into the body of the porridge and are batel to it, retaining no independent standing of their own. What lies in the dish is therefore one unified food, so a touch anywhere in it lands everywhere in it.
Porridge of chullin with terumah ingredients
"Hamikpah shel chullin, vehashum vehashemen shel terumah, shenaga tevul yom bemiktzasan, lo pasal ella mekom maga'o." When the porridge itself is chullin and it is the garlic and the oil that are terumah, and a tevul yom touched part of it, he has disqualified only the spot he touched.
In this case the reckoning runs in reverse. True, the terumah seasoning was stirred into a body of chullin, but terumah does not get cancelled by the chullin surrounding it; it holds onto its own identity instead of dissolving into the dish. Since it never truly merged with the porridge, contact at one spot does not carry across the whole, and nothing beyond the place actually touched is disqualified.
"Ve'im hayah hashum merubah, holchin achar harov." If the garlic was the greater part of the mixture, we follow the majority, and the dish is judged accordingly.
Rebbi Yehudah's qualification
"Amar Rebbi Yehudah: eimasai? Bizman shehein gush baka'arah." Rebbi Yehudah asks when this halachah applies, and answers: when the ingredients form a single mass in the bowl. Then they truly are one dish.
"Aval im hayah mefuzar bamdochah, tahor, mipnei shehu rotzeh befizuro." But if the mixture lies scattered in the mortar, it stays tahor, because the owner wants it scattered. When a person deliberately keeps the pieces apart, expecting them to remain distinct, they are not treated as one body. Touching one portion disqualifies that portion alone and reaches no further.
Other foods pounded in a mortar
The Mishnah now broadens the ruling: "Usha'ar kol hanidochin shedachan bemashkin." Every other food that is crushed in a mortar is governed by the same standard, provided that liquid was present while it was being crushed. The liquid welds the fragments into one another, and the contents of the mortar are therefore reckoned as a single item of food.
"Ve'es shedarkan liduch bemashkin, vedachan shelo bemashkin, vehein gush baka'arah, harei eilu ke'igul shel develah." Foods that are customarily crushed with liquid added, which on this occasion were crushed dry, and which are nonetheless sitting in the bowl as one lump: their din is that of an igul develah, a pressed disc of dried figs.
The comparison is instructive. In a cake of pressed figs the figs have been packed one against the other into what looks like a single solid block, and yet each fig retains its own identity and they are considered separate foods in halachah. So too here. Since this food is ordinarily prepared with liquid and the liquid was deliberately omitted, we assume the omission was intentional, that the owner wanted the pieces to keep their individual character. They may be clumped together in the bowl, but halachically they remain distinct. Therefore if a tevul yom touches one of them, the tumah does not travel to the rest.