Midrash for Chullin 70:35
מאי לאו הא דם שחיטה מכשיר
and it would have been self-evident with regard to the blood of a dead animal! - It was necessary for him to state his view with regard to the blood of a dead animal,<span class="x" onmousemove="('comment',' That it cannot render foodstuffs susceptible to uncleanness.');"><sup>13</sup></span>
Sifrei Devarim
"On the earth shall you spill it as water": Just as it is permitted to derive benefit from water, it is permitted to derive benefit from blood — Just as water renders seed susceptible (of incurring tumah), so, blood. Just as water need not be covered, so blood (that of a disqualified offering which has been slaughtered) need not be covered.
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