The magician introduces a key chain, which has a small mixed Rubik's Cube inside a small box.
The top of the box is a clear acrylic and the other 5 sides are colored in black.

Hand the box to the spectator and have them try to spin or turn the cube inside the box.
The spectator is unable to do so.

But when the box is handed back, the magician can turn the cube without any effort.
Show the spectator that the cube is slowly starting to be solved.
The box is handed to the spectator again to try.

The spectator cannot turn the cube.
Finally, the magician completely solves the Rubik's Cube with ONE shake.

The spectator can examine the box at the end of the performance.