Reference for Niddah 45:2

ולהכי אפניה רחמנא לבהמה משני צדדין כי היכי דלא נגמר מן מופנה מצד אחד

that in the case of beast the All Merciful made both terms available for deduction: In order that no deduction shall be made from one of which one term only is available for deduction.<span class="x" onmousemove="('comment',' Since such a gezerah shawah, as stated supra, could be refuted. ');">²</span>

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