“How did an egg get in there?”

Stocking up at the butcher shop for the holidays, we decided to try a pollo relleno (stuffed chicken). We had a choice: salado or dulce (salty or sweet). We chose the former, hearing that the latter had things like pineapples inside it. The guy helping us could have, but didn’t, explain what the salado stuffed shicken contained. Perhaps I should have known (ya think?).

Pollo relleno - stuffed chicken in Uruguay

Susan’s comment after cooking and cutting it open:  How did a hard-boiled egg get in there?

Seems like I should have a clever which came first? comment, but I don’t.