031: The ashes of a stove are always considered muchan.Rabbah: Stove ashes are considered muchan only for needs that are certain, not for something that is only needed in case of a safek [such as for covering the blood of a koy].
Rava: When people prepare things for their needs, they only prepare for vadai [certain] needs not for needs which are safek.Rava is following the principle which he set forth elsewhere: Rava: If one brought in dirt to cover excrement [perhaps a child will dirty the floor, and he will need this dirt to cover it up], he may use it to cover blood of a bird that is slaughtered on Yom Tov. But if the dirt was brought in to cover up the blood of a bird, it cannot be used to cover excrement [which was not a certain event].Neharbeloi [the Chachomim of that town]: Even if dirt was brought in to cover the blood of a slaughtered bird, it may be used to cover up excrement.
They said in Maarava [Eretz Yisroel]: This matter is debated by Rabbi Yosi bar Chama and Rabbi Zeira and some say: Rava brei d’Rav Yosef bar Chama and Rabbi Zeira: One of them hold that blood of a koy can be compared to excrement, while one holds blood of a koy is different [because excrement is more probable than koy].
A proof that Rava is the one who says “blood of a koy can be compared to excrement” - from Rava’s statement above. This is indeed proof.
Rami brei d’Rav Yeiva: Blood of a koy is not covered on Yom Tov (032) because of a gezeirah lest its cheilev be permitted [a Chayah is different from a Beheimah in that its blood requires kisui and and its cheilev - an issur kareis by Beheimahs - is permissible. If covering blood of a koy is permitted on Yom Tov, some might say that it is actually a Chayah and its cheilev is permitted].
Challenge: Then kisui of a koy should be forbidden on a weekday as well?
Resolution: During the week, we assume that he’s covering up the blood so as to keep his chatzer clean.
Challenge: What if he’s shechting on a dung pile, where he’s certainly not covering for cleanliness? Additionally, what about someone who comes and asks a sheila as to whether kisui is required, and we tell him to cover it up - wouldn’t that lead to peritting cheilev?Resolution: In the weekdays we trouble everyone to do the mitzvah of kisui even though it is only a safek, but on Yom Tov we do not make people work because of a safek. 
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