Animal know when they are treated unfair. Read my article for "The Conversation": 

https://theconversation.com/animals-know-when-they-are-being-treated-unfairly-and-they-dont-like-it-73152

This article has been published by various print-media: 

http://www.iflscience.com/plants-and-animals/animals-know-when-they-are-being-treated-unfairly-and-they-dont-like-it/

http://www.independent.co.uk/news/science/animals-know- when-they-are-being-treated-unfairly-and-they-don-t-like-  it-a7592881.html