A spectator opens a bottle of water and turns it upside down. The water stays in the bottle. The magician suggests that, to make the effect even more striking, the spectator should perform the same action again, but this time with the water bottle's cap removed! Sure enough, even without the cap the water stays in the bottle. The magician then instructs the spectator to give the bottle a little squeeze, and this sends water streaming out of the bottle, all over the spectator's shoes.
Magician Dan Hauss invented the principle behind Flow (and named the effect after his Aunt Florence, "Who was just like my mother's sister to me.")
The effect is striking and leaves spectators amazed, amused, and somewhat damp about the feet and ankles. It is also quite easy to perform.
The secret behind Flow is a simple plastic insert that is exactly the same size and shape as the water inside a standard water bottle, but it has no opening at the top. The gimmick is filled with water to give it the weight and sloshiness of the real thing.
To perform the effect, the magician prepares the water bottle by removing its water and inserting the Flow insert. The bottle can now be given to a spectator, and no matter how invertedly the spectator holds the bottle, the plastic-entombed water will not escape. At the climax of the trick, the spectator squeezes the bottle, causing a specially constructed weak point at the top of the insert to burst and letting the water flow out normally.
Because the special insert is broken at the end of the effect, a new one must be purchased for each performance, but fortunately they are inexpensive. Magicians who want to perform this effect impromptu will need to hide a variety of water-filled inserts about their person so that they are prepared for any type of water bottle a passing potential spectator might be holding (the vast majority of common water bottle types can be covered with a collection of only 15 Flow inserts).
Note: Flow inserts are available in a number of custom sizes and shapes, including inserts for military canteens (great fun on the battlefield), bottles of holy water (perfect for Halloween vampire hunts), and various standard swimming pools (inverting the pool to show that the water won't come out is the magician's problem).