a necker cube is an example of a(n)
Necker cube The Necker cube is an optical illusion first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker.[1] It is a simple wire-frame drawing of a cube with no visual cues as to its orientation, so it can be interpreted to have either the lower-left or the upper-right square as its front side. Necker cube is used in studies of human visual perception.
Codd-neck bottle The Codd bottle was designed and manufactured to enclose a marble and a rubber washer/gasket in the neck. The bottles are filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle is pinched into a special shape to provide a chamber into which the marble is pushed to open the bottle. This prevents the marble from blocking the neck as the drink is poured.