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אלא שצריך להדיח כו'. וכ' הב"ח דדוקא כשהאחד מהן לח אבל אם שניהם יבשים אפילו הדחה א"צ: And the Bach writes that this is specifically when one of them has some moistness, however if both of them are dry, then even the act of washing it off is not necessary.