Reading to say, "And he shall look on the plague, and behold the plague," the Sifra interpreted the double allusion to teach that a sign of house plague was no cause of uncleanness unless it appeared in at least the size of "two" split beans. And because addresses the house's "walls" in the plural, the Sifra taught that a sign of house plague was no cause of uncleanness unless it appeared on at least four walls. Consequently, the Mishnah taught that a round house or a triangular house could not contract uncleanness from a house plague.