Garnishes are often thought of as little more than decorative embellishments, ornaments you add for aesthetic reasons. But in the world of cocktails, many garnishes are not just tinsel. Unlike parsley laid at the side of a meal, cocktail garnishes are tossed right into the drinkand a lot of them can be eaten, too. Some add so much character that the drinks they accompany are inconceivable without them. It is no surprise that the current cocktail renaissance has given the subject a fresh look. Wine Spectator's Jack Bettridge expalins.