Emotional stress comes from all sorts of relationships. Humans are a highly social species and the multitude of social relationships create a lot of emotions let that be good or bad. These emotions effect the physical body in many different ways. Bad emotions can create physical illness.
What really turned me off completely when I read that pigs actually eat their own faeces and other animals, sometimes including humans. I’ve done some research and found other sources saying the same. The obvious problem with pigs acting like this that there is a lot of contamination occurs and this has effects on many levels.