GEN1056 Among the laws of kashruth is the central prohibition against eating the flesh of an animal considered trefah, an animal which had a physical ailment of such seriousness that it would likely have died within a year. The Talmud and Codes enumerate in detail all the possible categories of physical disability and disease which render an animal trefah. Now, if a fowl has fallen and struck hard against body of water and it is uncertain whether the bird has sustained serious injuries, the Talmud gives a rule: See how it behaves in the stream of flowing water.  If the bird tries to swim against the tide, it will live. If the bird merely floats with the tide, it is mortally wounded! Hullin 51b.   So too with Jewry. Once free as a bird in our homeland, we fell and suffered severe bruises and wounds when our beth ha-mikdash, our Temple was destroyed and our land conquered, and our people sent into exile. And so, today, if an individual Jew fights the environment and swims against the mainstream, his Judaism lives within him. But if he takes the path of least resistance and simply flows along with the tide, then his Jewishness is fast ebbing away.   … Think back to the pleas of Abraham, trying to save the people of Sodom. The Almighty agreed at last that if there were ten righteous people among all the people of Sodom and Gomorrah, the cities would be spared for their sake [this verse].   Ten people could save two cities! Such is the power, the profound influence of those who can successfully withstand the influence of their milieu and rise above it.  If amidst the corruption and perversion of Sodom, a group of righteous ones can hold out and retain their piety, then all is not lost. SINAI1 238-9