There are those of you out there who enjoy a rare blueberry soda or peanut and jelly flavored beverage. Adventurous drinkers and Texas transplants who crave regional specialties can get their fix at Rocket Fizz, an eminently explorable shop in Deep Ellum. The 1,500-square-foot store, the third of its kind but the only one in Dallas, showcases hundreds of kinds of soda and an equally vast array of candy. Vintage signs and oddball tchotchkes can encourage loitering and impulse buys. But the soda selection is really the main attraction. Where else can one buy a bottle of Martian Poop marionberry flavored soda? And what the hell is a marionberry?