You show two clear empty glasses and a solid plastic square. The two glasses are stacked one on top of the other with the solid plastic square between them. Milk or any other liquid is poured into the upper glass and the liquid remains there as expected.
The glasses are now briefly covered with a silk or any such thing and in an instant the liquid from the top glass magically vanishes from the top glass and re-appears in the bottom glass. Seems like the milk has penetrated the top glass and the solid plastic square. Sounds impossible, but it has just happened right in front of the eyes of the audience!!!