Ask the Parent Wizard to fill the jug with hot tap water. Let the jug sit for about three minutes. Ask the Parent Wizard to pour out the hot water. Quickly reseal the jug. Watch the mighty invisible hand crush the jug.
Water is luckily one of the few things that expand when frozen.
There is a column of air about a mile high pushing down on you right now. That is about fifteen pounds per square inch at sea level. This means your body is pushing back with the same force. The hot water in the jug heats the air in the jug which pushes against that column of air. When the air inside the jug cooled, the air contracted, so there was less force exerted against the outside air.