According to Halacha one may slaughter animals with any tool as long as it is smooth and without flaws — a knife, a rock or stone, a reed, etc. The early sages gave this law and stated “One who slaughters using a rock or reed has made a valid slaughter.” Because it discusses the slaughterer, we see that this action is valid only after the fact, but is not the preferable method. The scholars noted: In a different place the early sages ruled that one is, even as a preferable method, allowed to use a rock or a reed. Answer: A rock or a reed which is not attached to the ground may be used for slaughter even as a preferable method, but if they are attached to the ground one should not slaughter with them. If he has already done the slaughter, after the fact it is validated. The scholars went on to ask: Did the early sages rule that a rock or reed attached to the ground is not a valid tool to use in slaughter? Answer: If the rock is connected to the ground because of its nature, like a cave rock or a very large reed and one used it for slaughter, placing the animal’s neck on the point of the rock, part of the cave, and led the animal back and forth, the slaughter is invalid, but if it is a rock or reed which have been disconnected from the ground and then reconnected, it is preferable not to use it for slaughter, but if it has already been used, the slaughter is seen as valid. In their opinion a distinction must be drawn between something which by its nature is attached and something which is artificially attached. The sages also made a rule about a wheel with a knife on its edge, whose turns are powered by a foot pedal like a potter’s wheel. If one puts the animal’s neck on the wheel’s knife to slaughter it, the slaughter is valid. But if the wheel’s turns are powered by a river’s flowing waters the slaughter is invalid, for the slaughter was not done by a Jew’s manual labor but by force of the flowing water. The sages added that if the river’s waters are dammed and a person opens the lock to make the water flow, turning the wheel and slaughtering the animal with the first turn, the slaughter is valid. But if the slaughter requires additional turns the slaughter is not valid, for the wheel’s subsequent turns are powered by the flow of water and not by the manual opening of the dam.
Thus, too, for the laws of murder. If a person ties someone up and leaves him in a dry water channel near the dam and then opens the dam so the water flows directly over the victim and kills him, the laws of murder apply. But if a person ties someone up and leaves him in a water channel far from the dam and then opens the dam, so the water flows along channel until it reaches the victim and kills him, the one who tied the victim up is exempt from the laws of murder, “Primary force is liable, secondary force is exempt.” Indirectly causing a death is exempt from charges of murder.
(Babylonian Talmud, Tractate Chulin 15b-16a)