(a) A Zav, a man who emits Zov two or three times, whether it is emitted in one day or in two or three consecutive days, is an Av ha'Tum'ah. (Zov is a clear discharge with the appearance of the white of a sterile or spoiled egg, in contrast with semen, which has the consistency of fresh egg white. Zov can also be a pus-like discharge resembling the liquid from barley dough or soft barley batter.)

(b) A Zav causes food items that he touches to become a Rishon l'Tum'ah if they have had a Hechsher l'Tum'ah (see next entry). Even if he does not touch the food (as in the case of milking a goat), he is Metamei it through Heseit, otherwise known as Tum'as Masa, if he is carries it or causes it to be moved.

(c) A Zav, Zavah, Nidah, and Yoledes who moves a person or object that is Tahor is Metamei the person or object. (Only Zav, Zavah, Nidah, and Yoledes can be Metamei people or objects in this manner.)

(a) Foods become Tamei if they touch a source of Tum'ah, but only after they first become wet by coming into contact with one of seven liquids: water, dew, oil, wine, milk, blood, and honey. Making foods wet in a manner that enables them to become Tamei is called "Hechsher." After Hechsher, even after the foods dry they can still become Tamei.

(b) The food can only become Tamei if the owner of the food was pleased with the liquid that wetted his food. This is learned from the Pasuk "v'Chi Yutan Mayim Al Zera..." - "If water has been placed on seeds and then the dead body [of a Sheretz] fell upon them, the seeds are Tamei" (Vayikra 11:38). The word "Yutan" in the Pasuk is written without a Vav and can therefore be read, "Yiten" - "he places." However, according to the Mesorah it is read "Yutan" - "it was placed." From this we learn that water or other liquids that fall on the food must be desirable to the owner of the food, as though he himself applied them.

(c) It is necessary only for the owner to desire the liquid; he need not desire that the liquid come into contact with the food. That is, even if the owner desires the liquid for an entirely different purpose, if the liquid later comes into contact with food it will enable the food to become Tamei. On the other hand, if the owner only intended to dispose of the liquid it does not enable the food to become Tamei, since only liquids that are significant can cause Hechsher.