Brain death (presumably) occurs as the chicken heads are passed between electrified brushes. Sometimes their beheaded before they are plunged into scalding water and a system of beaters to remove feathers. This isn't shown here.
In egg farms, chicks are sorted into male and female, and the males are ground up, alive. Transport to chicken meat farms would cost more than their meal is worth. Semi-humane death is for the more mature chickens we eat.
I knew all of these things and chose to still eat chicken and eggs, believing that their brief pain was matched by my life and pleasure. It took learning the consequences of animal protein and cholesterol consumption before I quit the same.