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The magician first shows a bottle filled with a beverage, along with a "transparent straw." Then, when the audience expects the magician to place the straw into the drink, they are surprised - it begins sucking up the liquid while held in the air, not the bottle! And, the liquid in the bottle gradually decreases! When the magician finishes the drink, he can temporarily freeze the drink in the straw, and then slowly allow it to flow out. 

Finally, the magician can magically produce an OREO chocolate! 

Both aspects of the straw look incredible - it filling up, and the glass or bottle's liquid level decreasing.