Reference for Chullin 217:20
<big><strong>גמ׳</strong></big>
<big><b>MISHNAH: </b></big>THE UDDER MUST BE CUT OPEN AND EMPTIED OF ITS MILK; IF HE DID NOT CUT IT OPEN<span class="x" onmousemove="('comment',' But cooked it together with all the milk it contained.');"><sup>10</sup></span> HE HAS NOT TRANSGRESSED THE LAW ON ACCOUNT THEREOF.<span class="x" onmousemove="('comment',' And no penalty Is 1ncurred either for cooking or eating the udder. The prohibition of 'flesh in milk' applies only to milk drawn off from the living animal but not to milk found in the udder of a slaughtered animal.');"><sup>11</sup></span> THE HEART MUST BE CUT OPEN AND EMPTIED OF ITS BLOOD; IF HE DID NOT CUT IT OPEN HE HAS NOT TRANSGRESSED THE LAW ON ACCOUNT THEREOF.<span class="x" onmousemove="('comment',' And is not liable to the penalty of kareth for eating blood. According to Rashi the Mishnah is referring only to the heart of a fowl and the reason why this penalty is not incurred is because the blood contained in the heart is not as much as an olive's bulk. According to Tosaf. it refers to the heart of any animal and there is no liability because blood that has been cooked is not forbidden by the law of the Torah. V. Ker. 220. The ckv flesh of the heart, says Rashi, is not rendered forbidden, for since it is smooth it does not absorb the blood. V. however Tosaf. s.v. .');"><sup>12</sup></span>