Chullin, Chapter 1, Mishnah 3. The chapter has been occupied until now with who is qualified to slaughter; it turns here to the question of where along the neck the knife must pass. Two Tannaim debate a case in which the blade enters inside the valid region and comes out just above it.
The Simanim and the Permitted Zone
For a shechita to be halachically valid, two organs must be severed: the windpipe (the kaneh) and the food pipe (the veshet). It is not enough that they be cut somewhere along their length. Each pipe has a defined section within which the cut must be made. A cut placed higher than that section, or lower than it, renders the shechita invalid. This defect is called hagramah, from a root meaning to tilt: the knife was angled off course and ended up passing through the wrong stretch of the pipe.
To understand the dispute, picture the anatomy of the windpipe. It is ringed by bands of cartilage, and between one ring and the next lies a thin layer of skin. The uppermost of these rings, the one closest to the head, marks the ceiling for shechita. A cut made above that ring is a problem. A cut made through the ring itself is perfectly acceptable.
A Cut That Ends at the Very Top
Now consider a shochet who inserted his knife within that highest ring, but held it on a slight angle, so that by the time the cut was completed it had drifted above the ring. Has he slaughtered properly, or has he committed hagramah? That is precisely the case our mishnah addresses.
The opening view, that of the Tanna Kamma, rules as follows. "Hashochet mitoch hataba'at": a shochet whose blade travels inside the ring, "veshiyer bah", and who leaves remaining within that ring, "melo hachut", a remnant as thin as a single hair, "al penei kulah", along its entire span, has performed "shechita kesheira", a valid slaughter. Picture a cut that crossed the full breadth of the ring while hugging its upper edge, so that a hair-thin strip of cartilage remains attached in the direction of the head, and that strip runs the whole length of the incision. Because not a single point of the cut escaped the ring, narrow as the margin was, the animal is kosher.
The reverse follows just as plainly. If even a small stretch of the cut slipped past the top of that ring, the animal is not kosher. According to the Tanna Kamma, the cut in its entirety has to stay within the zone allotted for shechita, with no part of it rising beyond.
Rabbi Yose ben Rabbi Yehuda's Leniency
The second Tanna takes a softer line. Rabbi Yose ben Rabbi Yehuda rules that it is enough to have "melo hachut", a hair's worth of cartilage left standing, "al penei rubah", over the greater portion of the ring rather than all of it. Practically speaking: a shochet who sliced through most of the topmost ring and only afterward allowed his knife to climb above it has slaughtered validly. In his opinion, once the greater part of the cut was executed in the proper section, what the blade did beyond that section afterward causes no harm.
The Principle Beneath the Dispute
The two views rest on a deeper question about what shechita is. Rabbi Yose ben Rabbi Yehuda holds that shechita requires the severing of only the majority of each pipe. Once that majority has been cut, the act is complete: the animal is permitted even if the cut was never finished, and anything that goes wrong afterwards is simply disregarded, since nothing further was needed.
The Tanna Kamma does not dispute that severing most of each siman suffices. His position is that whatever the shochet keeps doing with the knife is still part of one and the same act of cutting. Consequently, even where everything until that point was done flawlessly, and even though he was free to stop and leave a kosher animal behind him, a flaw that appears in the closing portion of the cut is a flaw in the shechita, and it is capable of ruining the entire slaughter.