Instead of an egg name something you'd be surprised to find inside an eggshell?

A chick. I get this joke and it's pretty funny. You would be surprised to find a chick in an eggshell. For those who don't get it (chick as in a term for girls/women). For an example sentence, "Look at that chick walking."

It's "chick" when you are using the term for both a girl and a baby chicken. Anyway, it would be surprising to find anything inside of an egg that isn't a chick or a part of the egg's original contents.

However, it would be surprising if you found a chick of any sort, and in any condition, in an egg purchased from a supermarket.

Not necessarily humorous, however, spies were known to imbed secret messages inside an eggshell, without breaking the shell!