The Shechitah Process

The Shechitah Motion

1. Shechitah must be performed by cutting in a drawing motion, not a chopping, as that would be a [Derasa] issue.

Knife Lengths

1. When slaughtering animals, the length of the shechitah knife should be twice as wide as the animal's neck to ensure easy cutting of the simanim.
2. A knife used for birds could lechatechilah be shorter, but the minhag Ashkenaz is also to only use a knife that is twice the width of the bird's neck in length, regardless of whether one will be doing one pull or push or both back and forth movements. A knife that is too long could result in a Derasa, but bediavad if the shochet is careful it's ok or lechatechilah for a major need.
3. Regardless of knife length, one should still shecht back and forth in a sawing motion. Bediavad, if it's twice as long as the animal's neck is wide, the the shechitah is valid. If it is shorter, then the shechitah is invalid, as the Chachamim were certain a small knife would need extra pressure to go from one end to the other and that would be derasa, notwithstanding the shochet's defense that he didn't add pressure, because he won't realize necessarily.
4. The Ashkenazi custom is to only permit a small knife in a bath and forth motion if it's a little more than one neck width (with the skin and spine) of the animal in length; otherwise, it's invalid. Some say this stringency should be applied by birds, too, to avoid [Derasa] issues, except in cases of great financial loss when shechting geese and chickens. By small birds, a short knife would be even more of an issue of piercing and, therefore, invalid even bediavad without a knife two neck widths long. The shochet's defense that he was careful is irrelevant here.
5. When using a knife longer than twice the width of the neck, bediavad cutting either back or forth is fine even if the simanim are completely severed before the knife completes its first motion, since the knifes is valid for shechitah and one doesn't intend to be dores. Rather, the blade was simply sharp enough to do the job faster. The same is true for a small knife on birds: if one intends to go both back and forth and already succeeds in severing the simanim in just one motion, it's kosher. His intention was to cut in a sawing motion until he succeeds, and he did.
6. Small knives that are kosher bediavad also cannot have sharp points at the tips, as that would create a possibility of piercing and is, therefore, declared categorically invalid, regardless of the shochet's defense that he shechted properly. Covering the tip would not help in this case.
7. If the animal was decapitated in just one motion with a knife twice as long as it's neck is wide, some invalidated the shechitah out of concern that there must have been extra force, resulting in a derasa.

Animal and Knife Positions

Standing (Omedet) or Lying Down (Munachat)

1. Shechitah for birds may be done by holding the bird down and cutting by moving the knife or temporarily fastening the knife upwards or downwards and passing the bird's neck along the blade. This may not be done for animals, though, for fear of Derasa by the weight of the animal. Moreover, in order to avoid future pitfalls, there is a rabbinic decree prohibiting any animal meat shechted in this manner despite the shochet's claim that he did not violate Derasa. Some argue that holding the knife steady from below and passing the animal neck along the knife from above has the same status. On top of that, some are further concerned that shechting from below when the animal is stationary is also problematic, unless the animal's head is tied upwards. If it's standing freely or lying down, that could be an issue even Bediavad. Therefore, some argue that ideally one should only shecht the animalwhen it is lying down with the neck below or to the side of the knife and stationary as the knife moves. Alternatively, the head can be tied and pulled upwards.
2. In this context, all birds are considered the same and all animals (Behemot Gasot and Dakot and Chayot) are considered the same. There is no distinction by species.
3. In modern kosher slaughterhouses, the Derasa concern in shechitah omedet is negated since the animal’s head is comfortably supported by a specially designed apparatus. Therefore, national hashgachot concur that this is an optimal form of shechita. Another device used in some slaughterhouses is an inversion pen, where the animal enters and is gradually rotated until it is lying upside down. It allows the shochet to cut with the more traditional downward motion. This machine was originally invented in 1927, called the “Weinberg Casting Pen”, with improvements made over the years. High costs and reduced efficiency preclude smaller operations from using it.

Machinery

1. A knife attached to a wheel and spun by human power (kocho) is kosher for shechitah regardless of whether one is actively spinning the wheel or spins it and lets go. Nevertheless, some express concern that perhaps it's rabbinically prohibited lest it lead to using knives set in motion by other forces other than the shochet's. It goes without saying that the shochet would have a harder time maneuvering such machinery and risks ruining the shechitah.
2. A knife attached to a waterwheel would be invalid for shechitah, unless one opens a dam of water that goes forth and spins the wheel. Still, only the first spin from the water would be valid, and some further argue that the first spin is lechatechilah invalid. Some also limit the circumstances to those in which the wheel is very close to the dam: if the water flowed for a considerable distance until it reached the wheel, that would no longer be considered the shochet's force.
3. There is no room for leniency if the wheel is attached to the ground.

Credibility & Dispute

1. If a dispute arises between the shochet and others regarding the kashrut of a shechita he did/they witnessed, there is much debate about the kashrut of the meat, depending on the circumstances, such as what the Shochet claims the issues were, if he made any excuses or made any marks on the animal, etc.