Our Sages have taught: One may not flay an animal from the feet on holy days; likewise one may not flay from the feet a firstborn or dedications unfit for sacrifice even on a weekday.
Generally speaking, removing an animal’s skin was done by cutting it in a straight line along its stomach from its throat to its tail. Margilim, or flaying an animal from its feet, was performed without cutting the animal’s stomach so that the full skin would be preserved for the purpose of creating a bellows or a storage skin for liquids or small objects.
The Gemara explains that the reason that it was forbidden to flay an animal from its feet on yom tov is clear. Although slaughtering an animal was permitted on holidays for food, this method of skinning the animal involved unusual effort for which no permission could be granted.
Several different explanations were offered by the Gemara to explain why it should be forbidden in the case of a first-born animal or a sanctified animal that was found to be unfit for sacrifice. Ultimately the Gemara reports that amrei be-ma’arava – in the West, i.e. in Israel – in the name of Rabbi Avin, that skinning the animal in this manner appears to be performing work with sanctified animals. Rashi explains that this is not a true prohibition, since, strictly speaking, there is no prohibition to perform work with a sanctified animal after it is dead. Nevertheless, it appears to be an inappropriate action.
The term amrei be-ma’arava is found many times in the Babylonian Talmud introducing a teaching that was relayed to the Babylonian sages from their peers in the west, in Israel. Due to the value that the Sages placed on these teachings, as well as the recognition that the traditions in Israel differed from those in the Babylonian academies, it was important to the Sages to record the source of these teachings.