I don’t know about the brains part. Anyone who owns chickens know they don’t have any brains. That’s why they’re chickens. The head is free of feathers- that makes sense. I don’t think it’s because when they finish the head they are not hungry any more- sometimes after they kill one chicken and eat his head they do another one. Another thing I’m puzzled about is that an owl apparently lands outside my coop, then walks into the coop to do his dirty deed?? I thought owls and hawks kill mainly by the first swoop and strike?? My run is surrounded by electric netting so it’s not an animal. The open entrance to my coop is at ground level with no door. Of course, now it has a door, but fewer chickens.