During one of Twilight's visits to her friends through the mirror, she is confronted with information that leads her to question more about the differences between the two dimensions.
This, characteristically, begins to get out of hand when Twilight decides she must get to the bottom of it. And to be fair, how can she let it slide when Pinkie has done something that doesn’t make any sense for her? She must know how Pinkie can possibly have a boyfriend in that dimension.
Proofread by the wonderful Soren Mercer