I know that you know.
You don't know that I know that you know
But I know.

Except now I've told you that I know you know
So you know that I know that you know
Unless you don't realize that I'm writing to you
(But I am!)

And now everyone who reads this is going to be paranoid
Wondering what I know and if I'm writing to them.
(But I'm not writing to them - I'm writing to you!)