This game is played by creating a parallel universe with one difference to this one. The next poster will then state the result due to the difference, and make his/her own universe.
Example:
User 1: There is a parallel universe where people greet each other by smashing their knees together.
User 2: As a result, humans are no longer able to walk. There is a parallel universe where men have breasts.
There is a parallel universe where the sky is bright red.
As a result, humans lost the evolutionary arms race and all the deer are singing Rudolph the Red Nosed Human. Oh, and at the time of writing RayOfLight's Armatar is a leaping human. There is a parallel universe where homo sapiens sapiens was supplanted by a race of people whose minds are merged, by means of telekinesis, into a single vast intelligence.