via Mental Floss
[Egg inside an Egg] (Viewer #686,057)
"It's called counter-peristalsis contraction, and it happens when a second egg starts forming before the egg that precedes it exits the hen's reproductive system. In such cases, the new oocyte (the part of the egg that becomes the yolk) moves through the chicken's oviduct per usual, collecting membranes and albumen (the white part) along the way. If a fully formed egg has been contracted back into the oviduct from the uterus, the whites of the still-forming egg will amass around it."
6 hours ago