The act of training a pet, such as a dog or cat, is a two way street. On one level, we are teaching them the rules of the society they live in, our society. They are no longer allowed to do certain things, and required to do others. On another level, when you train (for example) your dog, you are setting up a common language between the two of you. In a sense, it is the two of you who are in training.

There are certain things that people do when training their animals that might seem cruel to someone who has never trained an animal. We yell at them, shove their noses in shit, and sometimes even hit them, or cause them harm in other ways. This should not be mistaken for abuse. In their natural world, the world that we have destroyed, that they will never live in, inappropriate behavior was met with physical harm. You wander into a strange territory, you'd better not get caught. You try to take someone else's food, and you'd better not get caught. This is all part of the language that you need to learn in order to interact with your pet. They won't know what the word "no" means until you translate it into something that they can understand, and then build an association.