Rabbah: A bird which was slaughtered before Yom Tov, may not be covered on Yom Tov. If one prepared a dough before Yom Tov, he may still separate Challah on Yom Tov.
Abuha d’Shmuel: If he prepared a dough before Yom Tov, he may not separate Challah on Yom Tov [the permission to separate Challah is only granted if the dough is formed on Yom Tov and there was no other time to separate the Challah].
Question: Would you say then, that Shmuel disagrees with his father Abuha d’Shmuel?Shmuel: In chutz la’aretz [where Challah is only d’Rabbonon] one can eat a loaf of bread [on Yom Tov] and leave over dough at the end so that he can take off challah after Yom Tov. [If the bread can be eaten without taking off challah, then Challah cannot be compared to Terumah which enables one to eat the food and taking Challah should be permitted on Yom Tov. So it appears that Shmuel disagrees with his father and holds that challah can be separated on Yom Tov].
Rava: Shmuel agrees that were he to proclaim a piece of the bread Challah on Yom Tov, it would become prohibited to non-kohanim [so even Shmuel agrees that a Melacha can be done on Yom Tov when the challah is separated].
The following sugya is based on the subject of Maaris Hoayin - making people think you’re doing an Issur.
Mishna:Beis Shammai: A ladder cannot be moved from one dovecote to another [because people may think you’re moving it to repair the roof - these were made from caked mud and needed constant repairs, as they would sit out on the roofs a lot]. But it can be moved from one window to another. Beis Hillel permits this [since it’s not the type of ladder generally used for repairs].
Gemara:Rav Chanan bar Ami: This discussion is only in a case where the ladder is stationed in the street. Beis Shammai holds, those who see will think he needs to plaster his roof and Beis Hillel hold they’ll see the dovecote and understand he wants to get a bird, but if the ladder is on private property, everyone agrees it’s permitted.
Challenge: Didn’t Rav Yehuda amar Rav say “Any case the Chachomim forbade because of Maaris Hoayin, appearances sake, it is forbidden even in a hidden chamber”. [So how can it be that Beis Shammai would go against this principle]? 
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