Tekhelet and Hilazon - Which dye is right?

(2) For these blemishes of the eye, one may slaughter the firstborn animal outside the Temple: The eyelid that was pierced, an eyelid that was damaged and is lacking, or an eyelid that was split; and likewise, one may slaughter a firstborn animal outside the Temple if there was in his eye a cataract, a tevallul, or a growth in the shape of a snail (Hilazon), a snake, or a berry that covers the pupil. What is a tevallul? It is a white thread that bisects the iris and enters the black pupil. If it is a black thread that bisects the iris and enters the white of the eye it is not a blemish.

§ The mishna included in its list of blemishes of the eye a growth in the shape of a snail, a snake, or a berry that covers the pupil. A dilemma was raised before the Sages: Is the snail mentioned in the mishna the same as the snake, or perhaps they are two distinct blemishes, and the mishna means a snail or a snake?

The Gemara answers: Come and hear, as Rabba bar bar Ḥana says: Rabbi Yoḥanan ben Elazar told me: There was a certain elder in our neighborhood, and Rabbi Shimon ben Yosei Lakonya was his name, and in all my days I did not pass before him. But once I did pass before him, and he said to me: Sit, my son, sit, and I will teach you one matter: This snail that you see in the eye of a firstborn is a permanent blemish, and it is permitted to slaughter the animal on its account. And this is also the snake mentioned by the Sages as a blemish.

Mishnah “He should not check his garments for lice nor read by candlelight,” etc. Even on weekdays it is forbidden since it is not decent. It was stated: One who checks his garments takes and throws away; only he should not rub. Abba Shaul says, he may rub and throw away, only he should not kill. Ḥizqiah said, one who kills a louse is like one who kills a camel. Samuel broke off its hands and feet and gave if to the children. Rebbi Yose ben Rebbi Abun put it in a flask.

Rebbi Simeon ben Ḥalafta said, did we not understand this from the Hilazon? Does the Hilazon have sinews and bones? But was it not stated: Any which has neither sinews nor bones does not live more than six months?

For Rebbi Yose ben Rebbi Abun said in the name of Rav Zevid, the Holy One, praise to Him, turns around His world once in seven years. Qamqama turns into Ḥu-Rav-Padah. Ḥar-Efer turns into Šer. The head louse turns into a scorpion and the one of garments into a lizard. A horse worm turns into a wasp, that of cattle into a bee. A male hyena turns into a female, a field rat turns into a wild boar. The spine of a fish turns into a centipede, of a human into a snake. When? If he does not bow down with his entire spine.