I have a Sussex that is constantly bullying her sister. Her sis will be sitting down in the shade and the sussex will come up and bite her head. She won't let go either! Her sis doesn't run away either. She squawks when she gets bitten and puffs up, but other than that just sits there and lets her sis bit her over and over. eventually she will get up and run away after a minute or two. They are both on the middle of the pecking order. The pecking chicken only acts that way towards her sister, but none of the other chickens. Can someone help explain this situation?