The game board for “Guess That Button.” The game show host gives Alice the game board, and Alice pushes one of the four buttons. Observe that there are exactly three edges (green, blue, or red) touching the button that Alice pushes. The game show host then gives the game board to Bob, and one of these three edges randomly lights up. It is Bob’s task to guess which button Alice pushes. A classical strategy has a maximum success probability of 5/6, but entanglement can increase this to about 90%.