I would make the case that a chicken fully understands the concept of pain, feels pain itself, and inflicts pain on other beings as a tool for maintaining a social compliance.

Just the existence of something like a "pecking order" should demonstrate all you need to know to understand that the chicken doing the pecking knows in advance that the peck will inflict pain on the one being pecked and that the inflicted pain will cause that animal to alter their behavior by either recognizing the authority of the one doing the pecking, or by challenging that authority.

The sweetest cat that I ever had, now enjoying her (9 - n) life somewhere else, was the one true queen and ruler of everything mobile or potentially mobile on our property. Scraps of paper thrown from redneck's trucks as they passed along the highway became objects of great amusement as she slapped them into compliance with what she considered to be their place in her personal space.

Mice, rats, birds, lizards, raccoons, opossums, squirrels, and all manner of insects were both entertainment and sustenance. She had no fear of anything and a great love for all the humans she had chosen to adopt. She was the top of the food chain at our place until I decided to raise chickens.

I purchased a dozen young hens, none of them taller than the cat, and kept them confined in a mobile cage that I moved around the property. I was hoping that I could one day use the grown chickens to help control the fire ant and grasshopper populations since chickens always seemed to me to be not only simple-minded, but single-mindedly focused on eating anything that moved.

The cat watched these birds with obvious anticipation of their eventual freedom. She would sit outside the screened cage and observe them scratching and pecking and could occasionally be seen with a paw extended into the cage in an attempt to touch them. Within the cage the birds adapted to each other and a sort of social pecking order developed where one bird grew to be the dominant bird and ended up controlling the others like her own personal flock.

In time, I released the birds from the cage and they adapted to life outside the wire. Several were killed by my two clumsy black Labs who chased them down and murdered them before I could jump the fence and stop the carnage.

They were all still relatively small and the cat finally had an opportunity to touch them and exert some level of control over them. She would place herself in a position where the birds had to pass and as they passed she would reach out and pat or slap them on the head. This was all fun and games for her. Passing her and being slapped was a sort of toll inflicted on the birds and once she had patted them down she would wander off to find something more interesting.

Finally Ruby, the dominant bird, decided that she had had enough of that cat's shit and as soon as she had been patted, she jumped onto the trailer beside the cat and pecked the cat hard on the head between the eyes sending the cat scooting across the yard like furred lightning putting as much distance between herself and the birds as she could manage. From that day on, the cat gave the chickens a wide berth and a healthy dose of respect. In fact, during one attack where we lost a couple of chickens to a hawk she rushed in to defend Ruby from the hawk.

Sadly enough, Ruby eventually was killed by a couple of loose dogs belonging to a neighbor and my poor cat, queen of everything in our local universe, had to be euthanized. After 14 years as an outside cat she was ready for a new start somewhere else. I hope she found a nice warm spot with lots of distractions.

This story got too long but the general summary is that a chicken knows pain, feels pain, knows how to use pain as a tool to force compliance and that anyone who doesn't know this needs to spend a little time watching them and how they interact in their social world.