On rare occasions, while cooking with chicken eggs, you may encounter twins—two yolks in one egg. But Twitter user @Umeboshi had a far more astounding encounter: she claims that of the dozen eggs in a carton, every single one had two yolks. Casey Baseel of Rocket News 24 suggests how this could have happened:
Egg farmers can tell whether or not a hen has laid a double-yolk egg without cracking it open. The shells of double-yolk eggs tend to be longer and more pointed than those of single-yolks, and the two yolks can also be seen when using a light to inspect the contents of the egg without cracking it.
Double-yolk eggs taste just the same as single-yolks ones, and some people actually feel lucky to discover one. Not everyone is left with such a positive impression, though. Some shoppers find them kind of gross, and so to avoid shocking their more sensitive customers, egg farmers generally remove them from any batches before they’re shipped to market, as pointed out by Mitsuko.