Originally published as "The World's Greatest Invention" in Approaching Magic, it's not a card trick, and not a coin trick. It's baffling, amusing, and astonishing. It can be performed for a room filled with sophisticated adults or at a kid show.
It's the kind of trick that you read in a book and think, "That's pretty cool." But then when you see it ... it jumps to life and makes you think, "I want to do that trick!" The problem is, it's a pain in the ass to get the props for it. Not now though; the whole package is available!
In effect, the magician hands one spectator a glass of liquid, and another a simple straw mat. He takes back the glass of liquid, hides it behind the mat for a moment... and it vanishes.
He shows both sides of the mat - the glass of liquid is simply not there. Then he reaches behind the mat and produce the glass, still filled with the drink.
He repeats the vanish twice more, escalating the impossibility and further confounding the audience. He shakes the mat - no glass, no liquid. He turns the mat sideways, rolls it into a tube... and reproduces the glass to a guaranteed ovation.
The glass is not gimmicked (use you own glass), nor is the liquid (you can really drink it) or the mat... but there is a gimmick and it has been beautifully realized.