In this demonstration, warm water is placed in a plastic syringe, the syringe is sealed, and the plunger is pulled back causing the water to boil. The water boils because the action of pulling back the plunger increases the volume, thus decreasing the pressure. The boiling point of a liquid is dependent on the pressure of the system, so a decrease in pressure leads to a decrease in boiling point.
When a marshmallow is placed in a large capped syringe and the plunger is pushed in, the air in the marshmallow contracts from the pressure. Conversely, if the plunger is pulled back, the pressure decreases causing the air in the marshmallow to expand.
When dry ice is placed in warm water it sublimes very quickly forming a large amount of carbon dioxide gas. When a bubble is placed over this the bubble grows from the pressure.