Probably just a meat spot. I have a hen that lays them consistentlyI am wondering the same thing! One of my girls, not sure which one, has laid eggs 2-3 times in the last year. (All my girls are 1-3 years old). Upon cracking the egg open, (which are refrigerated for about 4-5 days after laying), inside, much to my surprise was what appeared to be a flesh-like growth (attached to the yoke). It was not quite 1/4” in size. I’ve seen this 2-3 times in the past year, but don’t know which of my girls are laying an egg with something like that in it? I don’t know what to think of it? I have no roosters so don’t know how that is possible.