Midrash su Levitico 11:34

1) I might think that vessels, too, acquire tumah in the atmosphere of an earthen vessel. It is, therefore, written (Vayikra 11:34): "all the food … and all drink": Food and drink acquire tumah in the atmosphere of an earthen vessel, but vessels do not. I might think that animal food, too, acquires tumah; it is, therefore, written "the food," the distinctive food of human beings. I might then think that I exclude (from tumah) animal food that one thought to use for human consumption; it is, therefore, (to negate this) written "all food (… shall be unclean"). I might think that even foul food (that is not fit for dogs, is included for tumah); it is, therefore, written "which shall be eaten," to exclude foul food. "food … shall be tamei": We are hereby taught that any amount of food becomes tamei. I might think that any amount (of food that is tamei) can confer tumah upon others; it is, therefore, written "which shall be eaten" (in one swallow). Only the size of an egg can confer tumah (upon others).

1) I might think that even a gourd which fell into the atmosphere of the oven and was not predisposed (to the acquisition of tumah) would become tamei; it is, therefore, written (Vayikra 11:34) "upon which water came." This tells me only of water (as a predisposing element). Whence do I derive the same for dew, wine, oil, blood, honey and milk? From "drink" — this is wine; "that is drunk" — this is blood, as it is written (Tehillim 110:7): "From a river, on the way, shall he drink (blood), wherefore he shall lift (his) head." Whence are other liquids derived (as predisposing elements)? From "and every drink." If "every drink," I would think (even) mulberry juice, fruit-juice, pomegranate juice, and (the juice of) all other kinds of fruits. It is, therefore, written "water." Just as "water" is characterized by the absence of a qualifying epithet, so I include dew, wine, oil, blood, honey, and milk, which have no qualifying epithets, and I exclude mulberry juice, pomegranate juice, and (the juice of) all other kinds of fruits, which have qualifying epithets.

5) "And if water be placed upon a seed": This teaches us that a sheretz does not confer tumah upon a seed until it has been conditioned (to acquire it by water). — (But why is a verse needed for this?) Can it not be derived inductively? viz.: An earthen vessel confers tumah and a sheretz confers tumah. Just as an earthen vessel confers tumah upon seed only after it (the seed) has been conditioned by water (viz. Vayikra 11:34), so a sheretz confers tumah upon seed only after it has been conditioned. — Would you say such a thing? If you are lenient with an earthen vessel (which is only of first-degree tumah [rishon letumah]), would you be lenient with a sheretz (which is proto-tumah [av hatumah])? You would say that it confers tumah whether or not the seed has been conditioned! It is, therefore, written "And if water be placed … it is tamei," to teach us that a sheretz confers tumah upon seed only after it has been conditioned.