I was processing out some old hens that weren't laying or were teaching the younger ones to eat their eggs today, and one of them had a very strange growth inside. This was right above the vent once I cut inside and was sitting on top of all of the other organs (while laying on its back). I could feel it when attempting to grab under the breast bone but just thought it was a lot of fat until I got her open and saw how dark it was. I carefully took it out and then decided to throw out the whole bird due to not knowing what it was. Here are two pictures showing my hand for scale and then with it cut open. It felt like holding a deer heart and was quite heavy, relatively speaking. I've definitely not seen anything like it in any of our other birds. My thought was a tumor or an enlarged organ.