Reference for Chullin 94:5

בחזותא ואיכא דאמרי

Raba said: If [the lung was] blue it is permitted, if black like ink it is trefah; for R'Hanina said: Black [blood] is [in reality] red blood which has turned black by disease.<span class="x" onmousemove="('comment',' V. Nid. 19a. Hence black is a symptom of decay and disease. veurh');">²</span>

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