"La cola del perro" is that last of the stories in this collection, this one in the fable mode. A farmer is trying to maximize efficiency at his farm by making sure his animals are not goofing off. Since he doesn't have a good sense of how to judge their output, he decides to prohibit the dog from wagging his tail, under the theory that if the dog is wagging his tail he must not be working. The farmer goes so far as to threaten the dog with death if he will not stop wagging his tail.
The dog finds this very unnatural, but does learn that if he concentrates, grits his teeth and squeezes the right muscles, he can keep from wagging his tail. But he finds it very frustrating and stressful. As he becomes more stressed, his behavior becomes more hostile and threatening. Although the other inhabitants, including the farmer's wife, begin to think the policy has cost the dog his sanity. The farmer, though, thinks it is great, especially since a hostile dog makes for a much better guard dog.
Interesting story, which struck me either as a satire on workplaces that fixate on productivity or a commentary on communism. (They may seem like pretty divergent possibilities, but the Soviets were pretty fixated on productivity numbers in their days.)