Bekhorot 10B

הכא במאי עסקינן? כגון ששחטו להתלמד בו, ובפלוגתא דנימוס ורבי אליעזר.

The Talmud answers: Here, we are dealing with a case where he slaughtered the firstborn donkey in order to teach himself how to properly slaughter an animal, and not in order to eat it. In this case, R' Shimon and the Rabbis disagree whether the prohibition against a Jew’s consuming it serves as intent that it be treated as food. And they disagree with regard to the issue that is the subject of the dispute between Nimos and R' Eliezer.

דתניא, אמר רבי יוסי: סח לי נימוס, אחיו של רבי יהושע הגרסי, שהשוחט את העורב להתלמד בו ⁠— דמו מכשיר. רבי אליעזר אומר: דם שחיטה לעולם מכשיר.

As it is taught in a baraita that R' Yosei says: Nimos, the brother of R' Yehoshua HaGarsi, once related to me that in the case of one who slaughters a crow in order to teach himself how to slaughter a bird properly, its blood renders other foods susceptible to impurity, as blood is one of the 7 liquids that is capable of rendering foods susceptible to impurity. R' Eliezer says: The blood that comes from the slaughter of an animal always renders food susceptible to impurity.

רבי אליעזר היינו תנא קמא! אלא לאו איסורו חישובו איכא בינייהו.

The Talmud asks: Isn’t this statement of R' Eliezer identical to the statement of the first tanna, i.e., Nimos? Both hold that the blood of slaughter renders food susceptible to impurity. Rather, isn’t the difference between them with regard to whether concerning the crow its prohibition serves as its intent that it should be used as food?

תנא קמא סבר: דמו מכשיר לעלמא, אבל לגופיה בעי מחשבה.

Accordingly, the first tanna holds that the prohibition against consuming a crow does not render it a food. Therefore, its blood renders foods in general susceptible to impurity, but to render the crow itself a food, intent to eat it is also required, as people do not generally consume the meat of crows.