Related for Chullin 218:3

והא אנן תנן אינו עובר עליו מיעבר הוא דלא עבר הא איסורא איכא

Strictly it is not forbidden at all, but only because the second clause reads: 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, in which case it is true that there is no transgression of the law but clearly it is forbidden,<span class="x" onmousemove="('comment',' For although there can be no liability to any punishment for eating the blood in the heart of a fowl for the reason stated, namely that it is less than an olive's bulk, there nevertheless lies a prohibition even where there is less than an olive's bulk, and it would certainly not be permitted to be eaten.');">²</span>

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