Why is it that one molecule smells of spearmint, while its mirror image smells of caraway? No one knows. When scientists create new molecules in the laboratory, they may know every detail of a molecule's structure yet have no clue about what it will smell like.In theory you could assign a number to every discrete "odorant molecule" out there, though what a dreary wine-tasting guide that would make. Speaking of, I had forgotten all about the hilarious wine-tasting session in Brideshead Revisited: "It is a little, shy wine like a gazelle." "Like a leprechaun." "Dappled, in a tapestry meadow." "Like a flute by still water." You get the idea.