Show an empty glass, and then fill it with water or other liquid. Place a large playing card on the top of the glass.
Now turn the glass upside down, with the large playing card still underneath - the card adheres to the glass and doesn't fall to the ground! Remove the card, and the water now remains suspended inside the glass -- this looks incredible! At your magical gesture, the water finally falls down from the glass.
No external gimmick, use any glass. Simple and clean.
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