Concerned

[Wizwise2000]

Had my corn out today, handled her before I gave her a bath.
I had a peek at her belly, a little past half way to her tail there was a dark area, about the size of the end of a cigarette (maybe just a little smaller) in diameter. Just curious of what this is. I put her in a rubbermaid roughneck today with a little water at the bottom to hopefully loosen up the skin on her side. So anyways I looked in the roughneck to take her out. She had poo'd, so I thought maybe that's what I seen (I know, pretty stupid), but when I checked it was still there. Now is this dark "thing" supposed to be there? Or is this something out of the ordinary?
Could it be from constricting? She had eaten on the 15th and constricted the pinkie.

P.S It is not a growth externally, it is internal.

Thanks
Shane