Sifra: And the Torah writes "Rosho" to teach us that he is Tahor even if the hair of his head falls out and not of the beard.
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Why does the Torah refer to the back of the head as "Rosho" (S'tam), and the front, as "Pe'as Panav"?
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Oznayim la'Torah: Because whereas someone who sees someone head from the back will say that he saw his head, if he sees him from the front he will say that he saw his face - ssince the face attests on the person.
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