Halakhah su Levitico 10:20

Nevertheless, this conclusion, as well as that of Rabbi Landau, appears to be incorrect. In the above-cited ruling of Rambam, Hilkhot Ma'akhalot Assurot 3:8, regarding an unhatched embryo endowed with wings, Rambam rules that the unhatched embryo of a forbidden bird possessing wings is a sherez ha-of, i.e., a swarming bird-creature. That prohibition attaches to the unhatched creature despite the fact that its wings were never used and it never engaged in flight.⁸²Rabbi Friedman does take note of Rambam’s ruling and somewhat implausibly distinguishes the two cases: In the case of the unhatched bird, the embryo, if left undisturbed, will hatch and actually fly; the Anisakis however, is destined to be ingested by a larger fish and will never actually “creep” in water. It might be countered that, despite the grammatical identity of the two phrases, the phrase "mi-kol sherez hamayim"(Leviticus 11:10) translates literally as "of all that swarms in water" while kol sherez ha-of (Leviticus 10:20) should be translated as "all of the swarming birds," i.e., creatures having capacity for flight but not necessarily creatures that have flown. More likely, in both the case of a sherez ha-of and in the case of a sherez ha-mayim, it is the "to'ar" (to use the terminology of the Brisker Rav), i.e., the appearance or physical characteristics of the creature that are determinative rather than the actual performance of the activity common to such creatures. Hence, any organism having the appearance of a creature that "swarms in water" would be prohibited even if that creature has not actually swarmed in water.