Chullin, Chapter 2, Mishnah 8. Our chapter has been working through the ways a shechitah can be ruined, and here the Mishnah turns to a very different sort of flaw: not the knife, not the cut, but the intention behind it. What happens when an animal is slaughtered as an offering to something other than Hashem?
The Mishnah states: "Hashochet leshem harim, leshem geva'ot," a person who slaughters while dedicating the act to mountains, or to hills, "leshem yamim, leshem neharot," dedicating it to seas, or to rivers, "leshem midbarot," dedicating it to deserts, "shechitato pesulah," his shechitah does not stand. The meat is off limits, since the animal was killed as a sacrifice to avodah zarah.
Eating Is Forbidden, Benefit Is Not
There is an important limitation here. In all of these cases only the eating of the meat is forbidden; other forms of benefit from the carcass remain permitted. That is a striking exception, because the standard rule with an animal slaughtered for avodah zarah is that nothing at all may be derived from it, neither eating nor any other use. The cases in our Mishnah stand outside that rule.
The reason lies in the nature of these "deities." Mountains, hills, seas, rivers and deserts are all part of the natural world, attached to the ground itself, and in this context something bound to the ground is not treated as a genuine idol. On the level of Torah law, then, slaughtering to a mountain is not truly an act of idolatrous worship.
Why, then, is the meat forbidden at all? Because the Chachamim issued a decree. Their concern was that people should never come to eat meat that had been offered to avodah zarah. If the public were told that meat slaughtered for the sake of the sea, for example, is perfectly fine, the line would blur, and eventually people would find themselves eating meat that had genuinely been offered to an idol. To keep that from happening, the Sages forbade the eating here as well.
The Mountain Itself, or the Angel Over It
All of this applies only when the offering was directed at the mountain itself, at the physical feature of the landscape. If a person slaughtered to the angel appointed over the mountain, that is a straightforward case of avodah zarah in every respect, and no benefit whatsoever may be taken from the animal.
Two Holding the Knife
The Mishnah goes on: "Shenayim ochazim besakin veshochetin," where a pair of people hold one knife between them and slaughter together, "echad leshem echad bechol elu," with one partner directing the act toward any of the entities named earlier, "ve'echad leshem davar kasher," while his fellow directs it toward something permitted, "shechitan pesulah," the shechitah they performed together does not stand.
Even though only half the intention was directed toward avodah zarah, that is enough. Where idolatrous intent is involved we distance ourselves entirely, and the presence of that intent in even one of the two participants renders the whole shechitah invalid.