We used to have chickens when I was a kid -- actually ours were pretty humanely treated, as they were for eggs, not meat, and had a nice run, and were allowed out in the yard often as well. I did, however, also look after a chicken run much like one of those in the movie. There were there to provied eggs for the patients in the hospital.
Yeah, it wasn't pleasant. They were pretty cramped, and died quite frequently -- and then other hens weren't nice when you tried to remove the dead one and pecked at my hands. Plus the racket they made. We also would trim down there beaks and put it against a hot iron to stop it from bleeding. That is pretty necessary though when they are in such cramped condition because they will peck each other to death. The worse though was mucking the place out! Ugh! I was lazy too and would wait until the chicken shit was a couple feet high before mucking it out, and this was by hand with a shovel. When you turned over it over with a shovel there were maggots crawling throughout manure fat amd white. Lovely quite lovely -- plust when you just had it clean and as your were spraying it off they woulf of course shit on it again and start the same cycle all over.
I agree with OW you just dissociate. And honestly I hand't thought about it in quite a while -- and at that time I was completely vegetarian. Chickens really are stupid though, as one friend used to say: There's nothing wrong with eatin chicken beacuse they're as stupid as a cabbage.