Beitzah 7A

דפחיא למאן? יהבו ליה ביעי דשחוטה. אתא לקמיה דרבי אמי, אמר להו: מקח טעות הוא, והדר.

of a live chicken, who has? He sought to purchase eggs of this kind. They gave him eggs of a slaughtered chicken. He came before R' Ami, claiming he had been cheated. R' Ami said to the sellers: This is a mistaken transaction, and it is rescinded; the sale is void.

פשיטא! מהו דתימא: האי לאכילה קא בעי להו, והאי דקאמר דפחיא ⁠— משום דצריבן, למאי נפקא מינה ⁠— למיתבא ליה ביני ביני, קא משמע לן.

The Talmud asks: It is obvious that the transaction is void, as he specified exactly what he wanted. The Talmud answers: The ruling is necessary, lest you say that this individual wants them for food rather than for chicks, and that which He said: that he is looking for eggs of a live chicken, he said only because they are hard-shelled, mature eggs. What is the practical difference, i.e., what is this man claiming from the seller according to this rejected interpretation? He is merely demanding to refund him the difference in value between the two types of eggs. R' Ami therefore teaches us that the sale involved a fundamental error, as the eggs of a slaughtered chicken are unfit for incubation. The transaction is therefore void.

ההוא דאמר להו: ביעי דדכרא למאן! ביעי דדכרא למאן! יהבו ליה ביעי דספנא מארעא. אתא לקמיה דרבי אמי, אמר להו: מקח טעות הוא, והדר.

The Talmud relates a similar incident: A certain person said to vendors: Does anyone have eggs of a chicken that has had sex with a rooster? Does anyone have eggs of a rooster? They gave him eggs that a hen had absorbed from the ground, i.e., which had not been fertilized by a rooster. He came before R' Ami claiming that he had been cheated. R' Ami said to them: This is a mistaken transaction, and it is rescinded.