If you heat a knife to white-hot, the shechitah done with that knife is kosher, because it was already sharp enough before it was hot. The concern is whether the slaughtering was done with the knife's blade or if it was done via the heat and a burn. The Gemara contrasts the issues that pertain here to the details of tzara'at, which has a long-standing tradition "halakhah le-Moshe mi-Sinai" regarding the measure of impurity. Plus the details of shechitah as applied to a case of tzara'at. Also, the 3 knives that the butcher needs to cut the meat and the forbidden fats, and to keep the forbidden from contaminating the permitted. Plus, distinctive indications regarding which knife was which.