A balloon that enters alone into a bottle? This result reminds us the experiment "Imploding can". In that experiment, however, the water change from vapor to liquid is very abrupt. In contrast, in this experiment the evolution of the vapor condensation can be slowly seen, thanks to the low rate temperature change.

When the water inside the bottle is warmed its temperature increases slowly until ebullition temperature. Leaving the water in ebullition, during some time, the generated vapor will occupy, almost, all the inside bottle volume. After that, the balloon is placed in the bottle mouth to accompanying the vapor condensation evolution. Then, the temperature inside the bottle will decrease, making the vapor to condense. As the vapor is condensing, the balloon will occupy the volume that the vapor occupied in the beginning to compensate the pressure variation (low pressure inside). The balloon continues to be sucked until it stops when it's reached an pressure equilibrium between vapor and liquid inside the bottle. This experiment is an evident proof that a gas occupies more volume than a liquid. Try it at home, but be carefull with the hot glass!