Dilbert and Dogbert sit at a table in a restaurant. The waiter hands Dilbert the check and says, "I've taken the liberty of calculating a twenty-percent tip." The server continues, "It's written on the back next to a picture of a smiling diner . . . A fifteen-percent tip is shown by the picture of a guilty-looking diner." The waiter continues, "Below that is a picture of a diner and his dog with salad forks in their backs . . ."