I started to peel and separate this orange into segments when I found this inside. Its ridges were growing between the orange segments where the pith would normally be.

I started to peel and separate this orange into segments when I found this inside. Its ridges were growing between the orange segments where the pith would normally be. What is it?
The answer: Sometimes navel oranges can have a second orange growing inside the first one. This looks to be what happened here, but the second orange died and began to decompose.