Editing Lubavitch Shechita (section)

===== Setting Up and Checking the Knife =====
Setting up the knife for shechita is a unique craft, and checking it requires great yiras shamayim. This is a kal vachomer (logical deduction): regarding checking that indeed the majority of the siman was cut (and not just half), which is a check of something relatively clear and visible to the eye, the Torah warned to be extremely careful, as it says "And you shall distinguish between the pure and impure, and between impure and pure birds" - how much more so regarding checking the knife which is invalidated by the finest nick, and often involves extra effort in properly setting up the knife and especially in feeling - things that hang by a thread (depending on the checker's condition, whether his hand is warm or cold, and of course the level of yiras shamayim of the shochet).

Regarding the knife, the main emphasis on yiras shamayim is regarding the checking, and because of this even for the shochet himself - whom we trust for his shechita - it is proper in industrial mehudar shechita to appoint an additional checker whose entire role is to check the shochtim's knives that they haven't become nicked during shechita (and we don't rely on the shochtim themselves in case from the effort and distraction of industrial shechita which is usually done under output demands that can pressure the shochet, his mind won't be settled enough).

The knife must be checked before shechita, during shechita, and after it.