Zavim, Chapter Two, Mishnah Four
Today’s mishnah deals with how a zav defiles things.
1) A zav defiles the objects that are lain upon (or sat upon) in five ways, so that they defile people and garments: by standing, sitting, lying, hanging or leaning.
2) What he lies upon defiles a person in seven ways, so that he [in turn] defiles garments: by standing, sitting, lying, hanging, or leaning upon it, or by touching or carrying it.
Section one: A zav can defile things that are lain upon or sat upon (such as chairs and couches) even though he hasn’t touched them. The things that he defiles will then defile other people and clothing (see Leviticus 15:5-6).
The five ways are: standing (he stands on the object, even if he doesn’t touch it. Sitting and lying (even without touching). “Hanging” refers to a case where the zav is hanging because of the couch or chair. For instance, the chair is on one end of a balance and the zav on the other. If the zav is lifted up by the heavier chair, the chair is now impure. These five things are called “midras hazav.” The chair or couch is now a “father of impurity” and it will defile other people and garments. Note that simply touching something is not sufficienthe must do one of these five things.
Section two: The couch or chair (or other such instrument) upon which he lied or sat (or one of the other ways of conveying impurity listed above) will defile people such that they in turn defile garments. Note that if it defiles garments, these garments do not defile people.
The couch or chair defiles by standing on a person, by sitting or lying on a person, by being hanged by a person (see previous section) or by leaning on a person. These five are the same as those above. In addition, it also defiles by touching or by being carried by a pure person.