Alex tried to put filled with water balloon inside the jar, but he couldn't. So we heated the air inside the jar and it expanded. Once we put the water balloon on top it, the flame went out and the air in the jar started cooling and shrinking back to its old size. But the balloon didn't let any more air into the bottle and it got sucked in. Before doing this experiment we talked about the danger of fire and that only an adult should handle it.