- Shechting using the force of water (כח ראשון and כח שני)
A Baraisa states that if one shechts במוכני – with a wheel (by attaching a knife to a wheel which cut the animal’s neck as the wheel turned), his shechitah is valid. This contradicts another Baraisa which invalidates such a shechitah, and Rav Pappa answers that the first Baraisa’s case is סרנא דפחרא – a potter’s wheel, which is turned by hand and the shechitah is performed by human force, whereas the second Baraisa’s case is סרנא דמיא – a waterwheel, without human force, and is invalid.
Alternatively, both Baraisos discuss a waterwheel, but the shechitah is valid when the wheel was turned בכח ראשון – with [the person’s] primary force (i.e., the first burst of water which he released onto the wheel by lifting the barrier), which is considered his force. However, when the wheel was turned בכח שני – with his secondary force (the subsequent water flow), it is not considered human force, and is invalid. Rav Pappa draws a similar distinction regarding one who bound someone near a body of water, and released the water onto the victim, killing him. He is liable if the victim died with כח ראשון, because גירי דידיה הוא דאהני ביה – it was his “arrows” that impacted him, but is exempt for כח שני, which is considered גרמא בעלמא – an indirect cause.
- תלוש ולבסוף חברו regarding idolatry and הכשר זרעים
Rava says that תלוש ולבסוף חברו – something detached which he later attached to the ground is considered detached regarding עבודת כוכבים. If one worships a mountain, it does not become forbidden in benefit like an idol. Still, one who bows to his house does make it forbidden in benefit, proving that the house is considered detached regarding idolatry. Rava says that לענין הכשר זרעים – regarding produce’s susceptibility to tumah, it is a machlokes Tannaim if תלוש ולבסוף חברו is considered מחובר. Food is only susceptible to tumah if it was contacted by liquid, e.g., water, whose initial falling onto something detached pleased the produce’s owner (even if the water’s subsequent contact with his produce did not please him). A Mishnah states that if one overturned a plate onto a wall so the plate should be rinsed by the rain (which then dripped onto produce), the produce is מקבל tumah (since the plate is detached). If the plate was placed there to protect the wall from the rain, the produce is not מקבל tumah (since he is not pleased with the rainfall). These two cases have contradictory implications regarding intent to rinse the wall, and Rebbe Elazar explains that the two cases reflect a machlokes Tannaim (if a wall is considered attached). [Rav Pappa answers the Mishnah differently.]
- Shechting with a knife fixed into a wall
The Gemara discusses shechting with something תלוש ולבסוף חברו. Although a Baraisa teaches that נעץ סכין בכותל – if he stuck a knife into a wall and shechted with it, the shechitah is valid, שאני סכין דלא מבטל ליה – a knife is different, because he does not nullify it there (i.e., he does not intend for it to remain there permanently), so it is definitely not considered attached to the ground. Shmuel said such a shechitah is only valid שהסכין למעלה וצואר בהמה למטה – where the knife was above and the animal’s neck was below it, and he moved the animal’s neck back and forth against the knife. But if the knife was below and the animal’s neck above it, it is invalid, because חיישינן שמא ידרוס – we are concerned he might press the neck against the knife because of the animal’s weight, invalidating the shechitah. Rav Pappa says that the shechitah of a bird, דקליל – which is light, is valid even where its neck was above the fixed knife, since its weight will not cause it to be pressed against the knife.