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1. Juices that flow out of baskets of olives or grapes do not always cause Tum'ah.
2. Similarly, blood taken from a person for medicinal reasons does not cause Tum'ah.
3. If spinach is squeezed into a Mikvah so that the water changes color, the Mikvah is disqualified.
4. One may squeeze a cluster of grapes so that the juice goes straight into food, but not so that it remains juice.
5. Even so (#4), when a Zav milks a goat, the milk is Tamei even if it goes straight into food.
A BIT MORE
1. If the juices are going to waste, or the owner said that he does not want the juice, they cannot cause Tum'ah since they are not considered a desirable liquid.
2. However, if someone were to take blood in order that it should be consumed by some creature or for some similar purpose, then the blood would cause Tum'ah (see Me'iri).
3. This is because any liquid from which a Mikvah may not be made causes the Mikvah to become invalid if it changes the Mikvah's color (even when the foreign liquid is less than three Lug).
4. This is because juice that enters straight into food is considered food, not juice. Since no "juice" has been "separated" from food, there is no prohibition of squeezing.
5. In order to become Tamei, a food must first come into contact with liquid. In this case, the milk cannot be that liquid, because (as explained above in #4) the liquid squeezed into food is considered food and not liquid. The Gemara therefore explains that it is the droplet of milk that is on the nipple of the goat (and that is not destined for the food) which renders the milk Tamei as a result of the Zav's causing it to flow.
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