Four plastic cups of progressively smaller sizes are displayed on the table. The largest cup is shown to be filled to the brim with milk. The performer pours the milk into the next smaller cup—yet nothing spills. The milk is then transferred to an even smaller cup... and then again into the smallest cup of all.  Still, no overflow.
 
To the audience, it appears as if the full glass of milk has impossibly shrunk with each pour—right down to a fraction of its original volume. For added impact, the entire sequence can be performed in reverse, with the milk seemingly growing back to its full size.
 
It looks like real magic—and it’s incredibly easy to perform.