The bottle pictured above and to your right are both first season bottles with an "alternate" clear glass stopper. This stopper was used in at least 2 episodes in which the bottle was featured as floating in the air. I can only assume this stopper was used because it had some technical value in allowing the floating effect to work. You'll also notice the inside of the neck appears white ... I don't know why that is so. It is believed to be puddy or some material used to hold the stopper in place.
