Rava Sharpens His Knife on Yom Tov
Asked whether he is sharpening or cleaning his knife on Yom Tov, Rava says only cleaning, hiding a leniency that may be kept but not taught.
Rebbe Nechemiah the son of Rav Yosef said, “I was standing in front of Rava while he was rubbing a knife on the mouth of a utensil. I said to him: Are you doing that to sharpen the knife or to clean it? Rava replied, “I intend merely to clean it.” However, it was apparent to me that his intent was to sharpen the knife but he holds halachah v’ein morin kein.” The Gemara then proceeds to cite an almost identical story with Rabbah sharpening his knife and Abaye questioning him. Both Rabbah and Rava held that one is allowed to sharpen a knife under certain circumstances on yom tov but did not want this leniency to become known. Rashi explains that since the sharpening is only permitted in a specific scenario, people might err and unconditionally permit knife-sharpening on yom tov and thereby violate a biblical prohibition.