I dunno 1st chicken i ever saw getting offed was at the hand of my grandma. She lopped its head off with an ax and its remainder went running around throwing blood everywhere.
Impressive. I was 3, the fried chicken was still good though.
I remember seeing this early, also. What you do is tie one of the chicken's legs to a tree or any stable object. Then chop off it's head and it won't go far. Yea, it will flop around for about a minute, but no pain I'm sure. It is probably just the nervous system makeup.