Once my mother found a dirty paper towel in a factory sealed bag of potato chips. She took it back to the store and they let her exchange the bag for one without a paper towel.
On another occasion my husband found a piece of metal chain in his Krispy Kreme donut. They sent a representative to our house to pick up the chain. Oh, the rep brought my husband a new box of donuts.
By the way, no one actually ate the paper towel or metal chain.
But stuff that really shouldn't does gets into food. We as humans are obviously a tough lot or we would have died out a long time ago.
I laugh at the eggshell in your cake.