I adopted "Milky Way" from the local shelter, and was told he needed to be neutered before I could take him home.

I arrived to take him home, and was told, "the operation was great! She's in fine shape!"

I said, "She?? Are you sure the operation didn't go too far?"

Turns out "he" was "she" the whole time. "She" became "Leela" and has been with me for nearly 10 years.