I have 3 chickens all about 9 months old. 2 are laying eggs but one is not. She will go into the coop and sit like she wants to lay an egg and then she comes out leaving no egg behind. Once, I found an rubber egg in the coop but don't know which chicken laid it. I did start on oyster shells but they are not very excited to eat it. Today, my non-laying chicken went into the coop. When she came out, she started to pick up tiny branches and was swinging them around to her butt. She stopped after about 3 tries. She eats normally and she is very active. She is giving no indications of illness though she does seem to have a loose stool. Any suggestions.