Gosh my chickens get exercised and angry when I've done a general dusting. They hate me for days! So I'm imagining they might know about a cull. Don't you find yourself listening to the cadence of their little conversations, trying to figure out what they're talking about, and suspecting the worst?
Chickens will notice when flock members are missing, but I think they mainly seem "upset" because it changes their pecking order. Things are out of order, and they just need to readjust. They'll be over it in a few days. We don't kill them away from the flock when we butcher. We just grab the one we want, lop off the head and after things settle down, they go about their business.