A drunk shambled into a bar and bet the barman that he could tell the ingredients in any drink the barman cared to mix. The barman stooped behind the bar and emptied into one glass the remains of several drinks - a Martini, a Scotch and soda. brandy, a rum punch and so on. The drunk sipped the drink and one after another correctly named the contents. He offered to do it again, and this time the barman filled the glass with water. The drunk tasted it, thought reflectively, tasted it again and then said, 'I don't know what it is, but it won't sell.'