One of the examples that appears in the Mishna on yesterday’s daf of an abortive birth that is considered significant for the laws of tum’at yoledet – ritual uncleanliness following birth – is “a sandal fetus or afterbirth.” The Gemara on today’s daf discusses the appearance of a “sandal.”
Our Rabbis taught: A sandal fetus has a similar appearance to a certain fish of the sea known as a sandal fish. It looks as though it is a full-fledged offspring from the outset but it was mashed. Rabban Shimon ben Gamliel said: A sandal fetus has an appearance that is similar to the tongue of a large bull.
In the name of our Masters it was testified: For a sandal fetus to have the halakhic status of offspring it requires the shape of a face. Rav Yehuda cites Shmuel as teaching: The halakha is that a sandal fetus requires the shape of a face. Rav Adda citing Rav Yosef who had it from Rabbi Yitzhak ruled: A sandal must have the shape of a face even if only at the back, this being a case similar to that of a man who slapped his fellow and pushed his face back.
The “sea-fish” described as a sandal appear to be a flatfish (bothus) that lies flat on the ocean floor and has both eyes on one side of its body. (In Hebrew it is called dag Moshe Rabbeinu – “Moses’ fish” – since it appears to have been split in half with the splitting of the Reed Sea.)
The disagreement about the definition of “sandal” as a fish or the tongue of a bull appears to relate to both its name and to its appearance. The Sages identify it with a sandal-fish (described above) while Rabban Shimon ben Gamliel suggests that it looks like sandals worn on one’s feet, i.e., like the tongue of a bull. The Arukh LaNer notes that the Rambam (Mishneh Torah, Hilkhot Issurei Bi’a 10:12) identifies the sandal as having the appearance of the tongue of a bull. Given that there is no compelling reason to follow the opinion of Rabban Shimon ben Gamliel against the Sages, he explains that the Rambam apparently believes that there is no practical difference of opinion regarding the shape of the miscarriage, and the only argument related to the source of the name. The Rambam chose the example that would be more widely recognized.