Gemara

Question: Why do Chachamim hold that people do not save a Tamei Chagav (locust or grasshopper) for children to play with it?

Answer #1: They fear lest the child eat it.

Objection: If so, they should be concerned also about Tahor Chagavim!

Rav Kahana put Shushiva (a Tahor Chagav) in front of his mouth.

Rav: Remove it, lest people say that you ate it and transgressed Bal Teshaktzu (eating something disgusting)!

Answer #2: They fear lest it die, and the child will eat it.

109b (R. Chanina): One stung by a wasp should drink a tiny cup of 40 day old urine.

110a - Question (Ravina): May one drink urine on Shabbos?

Chulin 27a: "Ha'Tzon u'Vakar Yishachet... Degei ha'Yam Ye'asef" teaches that Asifah (gathering) suffices for fish. (They need not be slaughtered.)

67b: Worms underneath the skin in fish are permitted.

Ravina asked his mother to mix fish worms into his fish before he eats it.

74a (Mishnah): If one slaughters an animal and finds inside an eight month fetus (Nefel) dead or alive, one may eat it without Shechitah, just its blood must be removed;

77a (Mishnah): If one slaughtered an animal and finds a fetal sac, if it does not repulse him, he may eat it.

Kerisus 21b (Beraisa): Fish and Chagavim (locusts or grasshoppers) are wholly permitted.

This means that they are permitted without Shechitah.

Makos 16b (Rav Bivi bar Abaye): If one drinks from a bloodletter's vessel, he transgresses "v'Lo Seshaktzu."

Rishonim

Rambam (Hilchos Ma'achalos Asuros 17:29): Chachamim forbade eating food or drink that repulses most people, e.g. food or drink in which vomit, excrement or putrid fluids or similar things became mixed. Similarly, one may not eat or drink from dirty Kelim that revile a person, e.g. Kelim of the privy or glass Kelim used for bloodletting.

Rambam (30): Similarly, they forbade eating with filthy hands or on dirty Kelim. Bal Teshaktzu applies to all of these. One who eats these matters is lashed mid'Rabanan.

Rambam (Hilchos Shechitah 1:3): Fish and Chagavim need not be slaughtered. One may eat them alive.

Hagahos Maimoniyos (3): A Tosefta in Terumos permits eating Chagavim live or slaughtered. Actually, one may not eat them [live], for Bal Teshaktzu applies. Rather, if one ate them alive, Ever Min ha'Chai does not apply, for they need not be slaughtered.

Magid Mishneh: There is no proof from Shabbos. Some say that Shushiva is a Tamei species. Perhaps this is why Rav told him to remove it! Alternatively, the Rambam teaches only that they are permitted regarding Ever Min ha'Chai.

Note: Rav told him 'lest people say that you transgressed Bal Teshaktzu.' The Magid Mishneh holds that this could refer to "Al Teshaktzu... b'Chol ha'Sheretz..." (Vayikra 11:43)!

Radvaz: The Rambam permits eating limbs from them. Bal Teshaktzu applies to eating them whole.

Rashi (67b DH Ivla): Ravina asked his mother to mix the worms into his fish, lest he see them and be repulsed.

Tosfos (90b DH d'Lo): Even though one may not eat a live Chagav due to Bal Teshaktzu, one may cut off a limb and eat it through washing it (so it will not be disgusting).

Poskim

Rema (YD 13:1): One may not eat fish or Chagavim alive, due to Bal Teshaktzu.

Beis Yosef (DH v'Chasav): Ba'al ha'Itur permits eating them alive, unlike Rav Sadya Gaon who forbids them alive. R. Nisim supports this from the Tosefta (Terumos 9:6), which says that one may eat fish and Chagavim alive or dead, without concern. Also the Rashba brought the Tosefta. I say that Rav Sadya Gaon did not forbid due to Ever Min ha'Chai, rather, due to Bal Teshaktzu, like it says in Shabbos.

Kaf ha'Chayim (5): One may not put a live Chagav or fish in front of his mouth, lest people say that he ate it and transgressed Bal Teshaktzu.

Shulchan Aruch (2): If one slaughtered a Kosher animal and inside was a live or dead eight month fetus, one may eat the fetus without Shechitah.

Taz (3): Rashi (Shabbos 90b DH Iy) says that Ever Min ha'Chai does not apply to Chagavim, but Bal Teshaktzu applies. Here Bal Teshaktzu does not apply, for he takes the meat when it is alive, but he cooks it.

Shulchan Aruch (84:1): Sheratzim that grow in water in Kelim and pits that do not flow are permitted, even if they do not have fins and scales. Therefore, one may bend down and drink from them, without concern lest Sheratzim come to his mouth.

Taz (2): Isur v'Heter ha'Aruch (41:7) says that if they disgust him, or there is danger, it is forbidden due to Bal Teshaktzu. Also the Rambam and Maharshal say so.

Shach (3): The Shulchan Aruch connotes that there is no problem of Bal Teshaktzu. Sefer ha'Chinuch explicitly says so. The Rema (13:1) forbids eating live fish, but here he intends only to drink, and he does not overtly swallow fish.

Pri Chodosh (3): If there are small worms in the water that do not repulse people to eat them, it is permitted and Bal Teshaktzu does not apply. If there are worms that if one knew about them, he would surely refrain because they repulse him, but Stam, without knowing whether or not there are worms, he is not particular and he is not repulsed, also this is permitted. This is clear from Ravina. Even though the worms repulsed him, and he knew that they are inside, he was repulsed only when seeing them. He would eat them if he did not them. The same applies here. It does not depend on what repulses most people, rather, on the eater. Presumably, most people would not eat fish worms if they knew that they are there, due to disgust. Rav Nachman was not concerned for this, since he was not repulsed as long as he did not see them. We find this also in Chulin 77a. If one slaughtered an animal and finds a fetal sac, if it does not repulse him, he may eat it. A Kohen may suck the contents of the stomach of an Olah, if it does not repulse him (Avodah Zarah 29b). Most people would be repulsed. Even so, it is permitted for one who is not repulsed. However, what the Rambam brings [in Hilchos Rotze'ach], and the Shulchan Aruch brings them in 116:10, are forbidden to all, for they repulse everyone. We can learn also from infertile eggs. If a hen sat on them, within three days they are permitted to one who is not repulsed, like I proved above (66:13). After three days, they are forbidden to all for they are repulsive. Whatever people refrain from due to disgust, it is called repulsive, and one may not eat it, e.g. a mouse (Avodah Zarah 68b). If only an individual is repulsed, even though it is not repulsive to others, all the more so it is forbidden to him. This is only mid'Rabanan. The verse is a mere Asmachta.

Shulchan Aruch (116:6): One may not eat food or drink that repulses people, e.g. food or drink in which vomit, excrement or putrid fluids became mixed.

Beis Yosef (DH Kasav): The Mordechai (383) derives from the Gemara's question that surely one may drink urine during the week. We discuss one who is not dangerously sick, for if not, surely it is permitted on Shabbos! Since during the week it is permitted l'Chatchilah for a Choleh without danger for a cure, b'Di'eved we permit if a child urinated in a pot [of food].

Gra (19): Avos d'R. Noson (26:5) says that one who eats foods that his body cannot stomach transgresses three Lavim: he disgraces himself, and the food, and blesses an improper Berachah.

Kaf ha'Chayim (70): Maharil says that one should not take an insect off a Sefer with his hand, for this is repulsive. Rather, he shakes it off.

Shulchan Aruch (ibid.): Similarly, one may not eat or drink from dirty Kelim that repulse a person, e.g. Kelim of the privy or glass Kelim used for bloodletting. Similarly, one may not eat with filthy hands or on dirty Kelim. Bal Teshaktzu applies to all of these.

Beis Yosef (DH v'Asur): The Rambam holds that the Lav of Bal Teshaktzu is on the matters mentioned in the Parshah. These other matters are only an Asmachta, so one is lashed only mid'Rabanan, like for other Mitzvos mid'Rabanan. Alternatively, these matters are mid'Oraisa, but there is a tradition that one is not lashed for them.

Taz (6): I say that there are no lashes [mid'Oraisa] because it is Lav shebi'Chlalos (different Isurim forbidden by one Lav).

Yad Avraham: The Prishah (28) says that it is not Lav shebi'Chlalos, because all of them (Tamei species) are called Sheketz. The Isur of eating what is repulsive is a mere Asmachta. Tevu'os Shor (13:2) says that the Prishah overlooked the Semag; he agrees with the Taz, that it is a real Drashah, and it is Lav shebi'Chlalos. I hold like the Prishah, for the Poskim hold like him, and unlike Semag. Whatever is one name is not considered Lav shebi'Chlalos, e.g. in Makos 18a (regarding meat that left its place; see Tosfos DH v'Lilki) and Menachos 58b. (Tosfos DH Ein says that one is lashed for eating Chadash (grain harvested before the Omer) of bread, parched grain or soft grain, and for Ma'aser of grain, wine and oil, for all of them have one name (Chadash or Ma'aser).) The Rambam and Ramban say so (Sefer ha'Mitzvos Shoresh 9), and so the Kesef Mishneh (Hilchos Avodah Zarah 1:11) explains the Rambam. Tevu'os Shor asked from Sanhedrin 63a, which says that "v'Lo Sa'avdem" is Lav shebi'Chlalos [even though they are all called Avodah]. He overlooked the Ra'avad (Hilchos Avodah Zarah 3:9. He answered that "Zove'ach la'Elohim Yecharam" forbids all Avodos done to Hash-m in the Mikdash, and all other Avodos are included in v'Lo Sa'avdem.)

Kaf ha'Chayim (72): Perhaps bloodletting Kelim are forbidden even before they were used, lest onlookers that they were used and cleaned.

Eliyahu Rabah (170:23): Sefer ha'Gan says that one who overeats, even for a Seudas Mitzvah such as Shabbos or Yom Tov, transgresses three Lavim - Hishamer Lecha, Bal Teshaktzu, for he fills his stomach like an animal, and he may not bless Birkas ha'Mazon afterwards.