There’s a mystery in your grocery store. Chicken prices have been falling at a fast rate, while egg prices have been changing equally fast — in the opposite direction. Why is this happening? Marketplace took a look at the phenomenon and found that the problem lies in exactly how the avian flu hits.

Chickens are getting bigger. A lot bigger. A new study charts the growth of the bird to almost 5 times its size from less than 50 years ago. That change, due mostly to changes in breeding, has brought not only a meatier bird, though, but also one with some new health issues.