I have about 20 hens and they are not quite laying yet. One of them constantly makes this croaking brrrrrrrrrrrrrrraaaaaaak brrraaakbrraakbrraak sound. I've notice when she does this (which is almost all the time when they are up and active) the other hens all sort of twitch their heads, like a super quick shake motion. I thought I read somewhere that is something they do when they are afraid. Can anyone decode this chicken speak for me so I know why she is doing this and why it worries them?