The Mishnah teaches that if someone slaughters an animal for idol worship – e.g. for mountains, hills, seas, rivers or deserts – the shehitah is invalid. What if the animal that is slaughtered belonged to someone else? Is it possible to forbid someone else’s property?
Rav Huna teaches that if someone’s neighbor’s beast was lying in front of an idol, then as soon as he has cut one of the organs of the throat – either the esophagus or the trachea – he has rendered it prohibited. In contrast, the Gemara brings the opinion of Rav Nahman, Rav Amram and Rav Yitzhak who rule that a person cannot render prohibited something that does not belong to him.
Rabbenu Hananel suggests that even according to this last opinion, if the person performed a full act of shehitah, the animal would become forbidden. The Rabbis differ only with regard to Rav Huna’s ruling that a partial shehitah is sufficient to render the animal prohibited. Rashi disagrees, arguing that Rav Nahman, Rav Amram and Rav Yitzhak believe that if the animal does not belong to him, his actions cannot prohibit it. Rashi points out that the continuation of the Gemara tries to disprove their position by bringing a case of a wine libation that is forbidden, yet a wine libation is a full act of worship. If these Rabbis agree that a full act renders the animal prohibited, then the Gemara’s question would not make sense.
Another issue discussed by the rishonim is whether Rav Nahman, Rav Amram and Rav Yitzhak who rule that someone cannot prohibit someone else’s animal would permit the animal to be eaten. Most argue that slaughter with idol worship in mind cannot be considered proper shehitah, that is to say, that although his thoughts cannot render the animal prohibited, at the same time it does not render the animal kosher. The Rashba disagrees, arguing that if the animal does not become forbidden, it is permitted to be eaten.