of fathers of impurity" (, avi avot ha-tumah) like the corpse, as says, "whoever in the open field touches one that is slain with a sword, or one that died . . . shall be impure seven days," and from the words "slain with a sword," the Rabbis deduced that "a sword is like the one slain" (, cherev harei hu kechalal), and thus a utensil that touches a corpse is a "father of fathers of impurity" (, avi avot ha-tumah) like the corpse. And another utensil touching this first utensil is rendered impure — a "father of impurity" (, av ha-tumah) — and both utensils acquire a seven-day impurity. But the third thing in this series, whether a person or a utensil, is then rendered impure with an impurity lasting until the evening — a first-grade impurity (, rishon l'tumah). And the Mishnah taught that a case of corpse contamination of four things in succession (where three are rendered impure with seven-day impurity and one with impurity until the evening) occurs when a utensil touching a corpse is rendered a "father of fathers of impurity" (, avi avot ha-tumah) like the corpse, a person touching these utensils is rendered a "father of impurity" (, av ha-tumah), and another utensil touching this person is rendered impure with a seven-day impurity — a "father of impurity" (, av ha-tumah) — as the Rabbis read "And you shall wash your clothes on the seventh day, and you shall be clean," to teach that persons who have touched a corpse convey seven-day impurity to utensils. The fourth thing in this series, whether a person or a utensil, is then rendered impure with an impurity lasting until the evening — a first-grade impurity (, rishon l'tumah). The Mishnah taught that there are 248 parts in a human body, and each one of these parts can render impure by contact, carrying, or being under the same roof when they have upon them flesh sufficient that they could heal if still connected to a living person. But if they do not have sufficient flesh upon them, these individual parts can render impure only by contact and carrying but cannot render impure by being under the same roof (although a mostly intact corpse does). Ulla taught that the Rabbis ruled the skin of dead people contaminating so as to prevent people from fashioning their parents' skin into