It hasn't happened to us before, partly due to the type of chickens we have had before I suspect, but White has gone broody.
For the past week, she has been clamped to the nest bit of the coop, only coming out to feed and poo once or twice a day before rushing back into the coop and continuing her vigil. We have removed, over the past week, about a dozen eggs from under her. She has given up laying, but steals Black and Spot's eggs and sits on them.
We aren't quite sure how to deal with this. The special boxes and coops for broodies seem a bit cruel and also a bit of a pain in a small area like ours. We have tried to make life uncomfortable by removing more and more of the nesting straw (but we have to leave some as Black in particular is a bit rough when laying eggs) and replacing the eggs with freezer blocks from the freezer (as a substitute for ice eggs which we hear are effective). We also open the roof of the coop all day and are threatening to send in the cats, but still she sits.
A photo of the brooding one will follow when we get it off the camera - but think of our nice standard Light Sussex, then double her size as she puffs up in anger at being disturbed! Finally, as she flies out of the coop for her second feed of the day, picture her flying straight into the chicken wire fence - she has done that every day for the past week too!
And here is the picture of White in all her broodiness!