Quotation על שבת 165:1

If a zav [sat] in one scale of the balance, while food and liquids were in the other scale, [the latter become] unclean. In the case of a corpse, everything remains clean except for a man. This is [an example of] the greater stringency applying to a zav than to a corpse; and there is a greater stringency in the case of a corpse than a zav. For whereas the zav defiles all objects on which he sits or lies upon, so that these likewise convey uncleanness to people and garments, and he conveys to what is above him madaf uncleanness, so that these in turn defile food and liquids. Whereas in the case of a corpse no such uncleanness is conveyed. Greater stringency is also found in the case of a corpse, since it can convey uncleanness by overshadowing, and it defiles seven days’ defilement, whereas in the case of a zav no such uncleanness is conveyed.