The early sages ruled that a person who owns an animal is forbidden to take it out into the public domain on the Sabbath if it is wearing metal shoes as protection against the stones on which it walks, nor if it is wearing an amulet around its neck for healing. They worded their ruling as “nor an animal with shoes on its feet, nor with an amulet, though it is proven, and this is a greater stringency in the case of an animal than in that of a human being.” The scholars asked: The early sages ruled, in a different place, that a person may wear an amulet which he received from an expert in amulet healing. Why was it ruled that an amulet may not be hung around the neck of an animal, even if received from an expert? Answer: The early sages intended to forbid only amulets made by non-experts. The scholars continued to ask: The early sages used clear and unambiguous language: “nor with an amulet, though it is proven.” Answer: The early sages meant that the person making the amulet was expert in healing people, but not in healing animals. The scholars then asked: The early sages continued to formulate their prohibition and said “this is a greater stringency in the case of an animal than in that of a human being,” meaning that an animal is forbidden to go out with an expert’s amulet while a person is permitted to go out with an expert’s amulet. Answer: This sentence relates to the earlier law prohibiting taking out an animal wearing metal shoes, while a person is permitted to go out wearing such shoes.
If so, the words of the early sages “nor an animal with shoes on its feet, nor with an amulet, though it is proven, and this is a greater stringency in the case of an animal than in that of a human being” should be interpreted to mean no amulet, even if it was made by one expert in treating people, but an amulet by a person expert in treating animals is permitted. The greater stringency than for a person should be interpreted to refer to the earlier statement “nor an animal with shoes on its feet.” The scholars continued to ask: How is it possible that a person would be expert in writing amulets for human healing and not be considered an expert also for animals? Answer: Man is under the influence of the planets and his success may stem from this influence. Animals are subject to no such planetary influence so they require special expertise in amulets for their healing.
(Babylonian Talmud, Tractate Shabbat 53a-b)