These things are the bomb -- they have this odd closure method, where
the bottle is sealed by a glass marble in the neck. To open it you push down on the marble with a special plunger that comes with the bottle. Then as you drink, the marble rolls around in a little reservoir in the neck of the bottle.
They're Japanese (naturally) and at an Asian grocer near you. They taste decent too, like fizzy lemonade with a slight tang of Hubba Bubba bubble gum.