I was thinking about it for a long time. It's not original so there is a chance you saw this theory already.
In the next few chapters. Law might try to swap Kaido with someone/something but it won't work and Law will be shocked and think to himself "Ehh, I'm out of stamina, it's impossible to swap someone as big/strong for me, right now" but he will see Kaido and Big Mom laughing and he will scream what's so funny and in that moment Kaido or Big Mom will say: "What's wrong? You can't teleport me with your Ope Ope no Mi?".
Law will think to himself that name of his fruit is a common knowledge but he will get confused on how they know that he actually tried to swap Kaido just now and them Big Mom will drop info bomb:
"That's right, the Surgeon of Death. I know this fruit and so does Kaido! In fact your fruit is the reason why he cannot be killed by anyone and anything right now. The secret of the World Strongest Creature... Immortality Surgery". Supernovas in shock!
Break next week...