Curious About Chicken Anatomy: Indent On The Breast

[Fluffy_Butt_Hutt]

I've never seen anyone address this question properly, so is it normal? Only one of my chickens has a very noticeable indent right below the crop all times of day. It looks like a coin slot. There's a prominent and hard "bump" felt right next to it on their right breast in the front (this seems common with all my other chickens, just less prominent). I've looked up multiple chicken diagrams, but never really got the answer. What would I call it as? I'm not worried about her, just curious if there is another word for her coin slot!

As I write this she stands on my shoulder and screams, which is a normal for her