The following items reduce the [opening to less than a] handbreadth: Less than an olive-sized piece of flesh reduces [the opening if the source of tumah] is a quarter [of a kav] of bone; a piece of bone smaller than a barleycorn reduces [the opening if the source of tumah] is an olive-sized piece of corpse flesh; less than an olive-sized piece of corpse flesh; less than an olive-sized piece of carcass; less than a lentil-sized piece of sheretz; less than an egg-sized piece of food; grain [covering] the window; a thick spider web; the carcass of a kosher species of bird that was not designated [for food]; the carcass of a nonkosher species of bird that was designated [for food] but was not rendered capable of contracting tumah, or it was rendered capable of contracting tumah but was not designated [for food].