The Big Bang Theory Wiki

Amy and Sheldon playing Counter Factuals.

Sheldon and Amy have create a game called "Counter-Factuals," where they postulate a difference in the world that currently doesn't exist and pose questions to each other. The game can only be played by them because it requires that you know how the other person thinks thus proving that they are very compatible together. Leonard tries the game and fails miserably. Asked that in a world where mankind is ruled by a giant, intelligent beaver, what food is no longer consumed? Leonard's answer is cinnamon, but the correct one is cheese Danish, as the people would build many dams to appease their overlord and flood the city of Copenhagen, devastating the Danish people enough to never invent their namesake pastry. Sheldon and Amy offer to play hide and seek with him.

Note: The Danish people did not invent the Danish pastry. Furthermore, the canals in Copenhagenis connected to the sea and not streams thus erecting barricades would not flood the city.