Commentary for Avodah Zarah 45:4

Ravina solves the contradiction by distinguishing between the ab initio law and the ex post facto law. Ab initio one should not leave non-Jews alone with animals. Ex post facto if they were left alone, we are not concerned lest they engaged in bestiality with the animal. Therefore we can buy the animal and use it for a sacrifice.

The Talmud tries to use two seemingly contradictory mishnayot to demonstrate that there is a difference between ab initio, when we are not concerned for sexual misconduct, and ex post facto, where we are not concerned. Ab initio a woman should not be alone with non-Jews — we fear that they will rape her But ex post facto, if she was alone with them because she was imprisoned for monetary matters, then she is still permitted to her husband. We are not concerned that she willingly had sex with them (which would cause her to be prohibited to her husband, even if he is not a priest).

The Talmud rejects the broad conclusion that ex post facto we are not concerned with sexual sin (bestiality or fornication). The reason why the imprisoned woman is permitted to her husband is not that this is an ex post facto question. Rather, she is permitted because the non-Jew will fear raping her lest this causes him to lose his money (the husband would not want to pay to have her redeemed, I know this is awful). This can be shown from the end of that mishnah, which teaches that if she was taken prisoner for a capital charge, she may not return to her husband. Thus the distinction is rejected.

Pedat solves the contradiction by attributing the sources to different tannaim. R. Eliezer holds that we are concerned about bestiality and therefore one cannot buy a red heifer from a non-Jew. He would also hold that an animal should not be left alone with them. The other sages are not concerned about bestiality.

The Talmud points out that the issue in that mishnah may not be the concerning for bestiality. It could be a concern lest the non-Jew had used the red heifer for work, for even the smallest load placed on the red heifer disqualifies her from being used in the purificatory ritual.
The “calf” referred to here is the calf used in the ceremony of breaking the neck and pouring the blood into the river to expiate for an unknown murder (Deuteronomy 21).

The Talmud rejects this proposal—the non-Jew who has a red heifer would know that he could sell it to the Jews for a huge amount. He would not risk this amount for the sake of carrying on it a small load.

But the same could be said about bestiality. The non-Jew would know that if he has sex with the animal (and gets caught) he could not sell it to the Jew. Therefore, he would not risk the financial loss. The answer is that while he knows this, his inclination could overcome him and he would engage in sex with the animal. Therefore, R. Eliezer is concerned about bestiality.

Shila suggests that the reason R. Eliezer does not allow one to purchase a red heifer from a non-Jew is that the verse which begins this chapter starts off with “speak to the children of Israel.” Thus he is not concerned lest the non-Jew engage in bestiality with the heifer.

The Talmud now rejects Shila based on the continuation of the mishnah. R. Eliezer does not allow one to buy any animals for sacrifice from non-Jews. Yet only with regard to the red heifer does the verse state explicitly that only an Israelite must bring it. Therefore, R. Eliezer’s reading cannot be based on that midrash. It must be that he is suspicious about bestiality.

The Talmud now tries another tack. Maybe the rabbis too are concerned about bestiality. But they assume that a non-Jew will not have sex with the red heifer because that would be a great loss. But when it comes to other sacrifices, maybe they would have sex with the animal. After all, it’s not such a big financial loss if the Jew won’t buy it.