Sanson: May I have my bill, please? 
Millicent: That's $20 in all. 
Sanson: Well, I am afraid you have made a mistake. Would you check it again, please? 
Millicent: Let me see. I am terribty sorry, sir. That should be $18. 
Sanson: It doesn't matter. 
Sanson points out a mistake on Sanson's bill.