Bruce King has an informative photo essay showing the use of pigs to recycle food that but for them, would be wasted.
Looking at the photos, I recognize certain behaviors - e.g. dominant pigs taking a spot directly under the tractor's bucket, resulting in them getting covered in food. It is even more ridiculous in real life. You might think they'd be scared of the big metal thing, or the hundreds of pounds of food that fall out of it. After a few times, they aren't afraid.
It is fun to watch the pigs feed. Like other important activities - breeding and fighting - they give tremendous focus.