Suppose you are sitting comfortably in your universe admiring the word SING. Just then, Q enters your universe and insists that you insert the string "IMMER" into your precious word to create a new word for his amusement.
Okay, you can make the word IMMERSING...
But then you realize, you can also insert "IMMER" into SING in a different way, to obtain SIMMERING.
One word, two possibilities... The universe bifurcates into two parallel realities, one with you holding IMMERSING and the other with you holding SIMMERING. We're through the looking glass here, people.
A similar phenomenon can occur if you are holding the word UNDAUNTED and The Master materializes into your universe and demands that you hand over the "UN" immediately. You could give him the first "UN", leaving DAUNTED. Or, you could give him the second "UN", creating UNDATED. Again, reality bifurcates.
And finally, as everyone knows, when you are confronted with a choice, the universe splinters into multiple parallel realities which follow each possible outcome.
Now that you know the mechanisms by which reality bifurcates, see if you can navigate the multiverse below, filling in words as necessary. (Click on the image to see a bigger image.)