The magician takes a glass, fills it with water, places a piece of cardboard on the glass, and then turns the glass upside down. The cardboard holds the water because of the vacuum inside the glass. But why doesn’t the water pour out when the magician takes away the cardboard? On the bottom of the glass, there’s a small hole that allows him to create the vacuum and hold or release the water. A transparent lid also helps the water to stay put.