When I said goodnight to my hens today, I noticed that one of them has a large fluid filled sac over her breast area. Looking at anatomy of chicken pix, it seems like it's her crop. When I palpated it, she didn't seem to mind, and she seems in otherwise okay health -- alert, eating and drinking, and laid an egg today. Are there possible ailments that are not too sinister? Is there something I should do? Thanks.