[The law banning a Jew from eating the sciatic vein in the thigh] applies to kosher animals, but not to nonkosher animals. Rabbi Yehudah says, it even applies to nonkosher animals! Rabbi Yehudah explains, wasn’t the sciatic vein banned already in the days of Jacob’s sons, when nonkosher animals were still permitted to them? They [the majority Sages] replied to him, [the law of sciatic veins] was given at Sinai, but it was recorded by God in its [narrative] context.
Genesis 32:32–33 explains that Israelites do not eat the sciatic vein “until this day” because of Jacob’s thigh injury when wrestling with the angel. After an animal is slaughtered, this vein with its blood must be removed from thigh of any kosher cattle. Because this process is difficult and thus costly, most kosher slaughterhouses sell the hindquarters to nonkosher companies. Rabbi Yehudah makes an odd claim—that this rule applies even to nonkosher meat. This seems to be nonsensical. Jews are forbidden to eat nonkosher animals, and non-Jews are exempt from the law of the sciatic vein! But his point seems to be that this law predated the laws of kosher animals, and therefore would have applied even before Mt. Sinai. The Sages reply that this, like all laws, came into effect only at Sinai, but that the Torah placed it in the narrative context of Genesis 32.