Man and utensils become roofs to convey tumah, but not to maintain something as tahor. How so? Four [people] are holding a slab of stone. [If there] is tumah below [the slab], the utensils on top of it become tamei. [If] there is tumah above it, the utensils underneath it become tamei. R’ Eliezer declares [them] tahor. [The slab] is placed on four utensils, even utensils made of dung, stone, or unbaked clay. [If] there is tumah underneath it, utensils on top of it become tamei. [If] there is tumah above it, the utensils underneath it become tamei. [The slab] is placed on four stones or on a living creature. [If] there is tumah underneath [the slab], the utensils on top of it remain tahor. [If] there is tumah above it, the utensils underneath it remain tahor.