If there were two people grasping a knife together and slaughtering an animal, one slaughtering for the sake of one of all those enumerated in the first clause of the mishna and one slaughtering for the sake of a legitimate matter, their slaughter is not valid.

GEMARA: The mishna states that if one slaughters for the sake of mountains or other natural entities the slaughter is unfit. The Gemara infers: It is unfit, yes; with regard to offerings to the dead, i.e., to idols, it is not in that category. Apparently, the status of the animal is that of an unslaughtered carcass, from which benefit is permitted, and not that of an idolatrous offering, from which benefit is forbidden. And the Gemara raises a contradiction from a baraita: With regard to one who slaughters for the sake of mountains, for the sake of hills, for the sake of rivers, for the sake of wildernesses, for the sake of the sun and moon, for the sake of stars and constellations, for the sake of Michael the great ministering angel, or even for the sake of a small worm, these are offerings to the dead, from which benefit is forbidden.

Abaye said: The apparent contradiction between the mishna and the baraita is not difficult. This mishna that teaches that the slaughter is not valid but benefit is permitted is referring to a case where one says that he is slaughtering the animal for the sake of the mountain itself, which is not an idol. That baraita that teaches that the animal is an offering to the dead and benefit is forbidden is referring to a case where one says that he is slaughtering the animal for the sake of the angel of the mountain. The language of the baraita is also precise, as the mountain and the other natural entities are taught together with and therefore similar to Michael, the great ministering angel. Conclude from it that the tanna is referring to slaughter for the sake of a spiritual entity, not the mountain itself.

Rav Huna says: If the animal of another was prone before an idol, once one cut one siman, the windpipe or the gullet, he rendered the animal forbidden. He holds in accordance with that which Ulla says that Rabbi Yoḥanan says: Although the Sages said that one who bows to the animal of another does not render it forbidden, if he performed a sacrificial rite upon it he renders it forbidden. The case cited by Rav Huna involves an action of that kind, cutting one siman; therefore, the animal is forbidden.

Rav Naḥman raised an objection to the opinion of Rav Huna from a baraita: One who unwittingly slaughters an animal that was designated as a sin offering on Shabbat outside the Temple, for idol worship, is liable to bring three sin offerings: One for performing the prohibited labor of slaughtering on Shabbat, one for slaughtering a sacrificial animal outside the Temple, and one for slaughtering an animal for idol worship. And if you say that once he cuts one siman he renders the animal forbidden as an idolatrous offering, then let him not be liable to bring a sin offering for slaughter of a sacrificial animal outside the Temple courtyard,