Explanation: When the bottle is warmed by the hot water, the air inside is warmed too. The warm air expands. When you set the bottle in cold water, the air inside is cooled, and the cooling air contracts. The air pressure outside the bottle is greater than the air pressure inside the bottle, so the air outside tries to move in. The balloon is then sucked in. This science trick works in the same way The Exploding Egg trick does.
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