Hartigan's Honor

I had this brainstorm a couple of days ago and it seems to have worked.

Me: Where's your overdue book?
Slacker child who never does what he's supposed to:  I don't know.  Probably at home.
Me:  What are you going to do about it?
Child: I guess I'll look for it.  If I remember.
Me: Let's go call home so your parents can remind you.
Child:  No! Don't make me call home.
Me:  Ok, let's make a deal.
Child:  *eyes me warily*
Me:  Repeat after me: I promise to bring my book tomorrow.  My word as Vorkos...I mean, Hardigan.
He repeats it.
Me:  You realize you just gave your word on your family's honor, don't you?
Child:  Um, ok.

He never did find the book but he did come in and pay for it the next day.