Shabbat 54 - What animal may not wear
If an animal wears something which it does not need, but which is there for the needs of its Jewish owner, then the owner made it carry something in the public area, and carrying on Shabbat is prohibited. What are the examples of such items? A camel may not go with a saddle cloth, since if it falls, the owner of the camel might carry it further. Nor may it go out bound (with its legs chained together) or hobbled (with its one lower foreleg bent upward toward the upper foreleg and tied). These cause pain to the animal, and are hence not welcomed by it and are a burden. In fact, this applies to any animal.
One may not tie camels to each other and pull one of them so that the others follow - because then he looks as if taking them to a marketplace for sale. However, he may gather their ropes into his hand and pull each one by his own rope - provided that he does not wind the ropes around his hand.
What is the reason for the last rule? This is talking about a special case when the rope is made of wool and linen - and one is forbidden to derive benefit, such as to warm his hand, from this combination. Wool reminds of Abel, who was a shepherd, and linen reminds of Cain, who worked the land, and the combination reminds of Cain killing Abel, so by refraining from this we correct his action in some measure.
Art: Belgian Unknown Masters - A Landscape With Camels