The question is if beasts of burden can go out in public wearing the standard control devices (bits, nose rings, halters and chains). The Mishnah gives specific examples – a camel with bit, dromedary with nose ring, “Lybian ass with halter” (the Babylonian rabbis have to translate what is meant) and horse with chain. Then goes on to include all animals which wear chains.
This is interesting because of humans (that is Jewish humans) cannot carry in public on Shabbat. Is a control chain on a horse considered “carrying?” The Mishnah says no – it is allowed.
The rabbis in their commentary expand the discussion to include muzzles. Hananiah permits them. Others question it. Does a cat, for example, need a muzzle when a chord is enough? (And did they really walk their cats with a leash?). Hananiah says: “whatever is an additional guard is not considered a (forbidden) ‘burden.’” The law follows Hananiah.
A charming story is told:
Levi son of R. Huna b. Hiyya and Rabbah b. R. Huna were travelling on a road, when Levi's ass went ahead of Rabbah’s. Rabbah felt insulted (thinking that Levi did this on purpose and acting disrespectfully to his elder).
Said he [Levi], I will say something to him, so that his mind may be appeased. Said he: “An ass of evil habits, such as this one: may it go forth wearing a halter on Shabbat?” “Thus did your father say in Samuel’s name,” [Rabbah] answered “The law is as Hananiah said.”
I love that the student, sensitive to the feelings of his elder, shows respect not by making excuses or acting defensively, but by asking a question and allowing his teacher to teach.