A stranger walks into a bar, looks at the board, puts $5 down and asks for a pint. The barkeep asks if he wants the Stout or the Amber. The stranger asks for the Amber.
Another complete stranger comes in, looks at the board, puts $5 down and asks for a pint. The barkeep immediately pulls a pint of Amber.
How did the barkeep know what the second stranger wanted?
Assuming prices differ, say Amber for 5 and Stout for 3.75<o:p></o:p>
customer put a 5 pound bill (paper!), while the second decided to pay in coins, placing
exactly the amount - no tip, mind you, thus avoiding
any further questioning.