Animals on Shabbos
6. It is forbidden for a person to lead two or more animals that are tied together, by holding onto the harness of one of them and automatically drawing the other(s) after it (1). This is prohibited even in a city with an "Eruv" (2). It is permitted to hold the reins of several animals in one's hand at one time and lead them in the manner described in the previous halacha (HY 87:5).
(1) Leading animals in this way makes it look like the owner is on his way to sell the animals in the markets on Shabbos. This type of prohibition is called "Ma'aris Ayin," and forbids doing anything that others might construe as a transgression.
(2) An "Eiruv" is an enclosure consisting of a series of poles or the like, with wire or string pulled tight over the top of them. It turns the area enclosed by it (sometimes even a number of neighborhoods), into a private domain ("Reshus HaYochid"), thereby permitting carrying within it.
(3) That is, one should hold the end of the rope so that less than a "tefach" protrudes from one's hand, and the part of the rope that hangs between one's hand and the animal does not reach within a "tefach" of the ground.