Mark:
There is this book, that I wanted... but I forgot what it was.
Clerk:
I've got it right here.(hands me the book)
Mark:
Thank you. I'll pay for it now.(hands her my credit card)
Clerk:
Thanks!(runs the card, prints the receipt, etc)
There you go!
Mark:
Thanks!
There was a guy nearby who watched and overheard this transaction, who looked really really confused.
What he didn't know, was that the clerk was my sister,
Sadly, I don't remember which book it was...