If Pit were to compare Dark Pit to something, it'd be a wolf.
The wolf was a mysterious animal- wild and free, leaping across the ground in endless strides. The wolf sang a song of melancholy, beautiful and fearful all the same. The wolf was a savage animal when forced to, ivory fangs bared like bone-teeth and stance curled back in aggression.
He thinks it's the perfect example of his counterpart, since he understands Dark Pit more than he knows. He picks up on the salt trails he leaves behind him when they exchange words, when they battle and move together as one. Pit knows Dark Pit is hiding in his own seclusion, in his own fear and he can tell by every subtle movement to his word choice.
It's odd, but Pit just knows because they're the same, one and the same, two halves of a whole. He thinks it's amazing in it's own beauty, but to this does it spark questions within his mind that he never did have much a chance to think upon with the fast-pace of the running war.
But, somehow, it's like Dark Pit understands that Pit knows about this. When Pit looks into his eyes, his dragon-fire eyes, he sees something different than the winter-ice he's familiar with.
Dark Pit may be the wild wolf and Pit may be the tamed dog, but there is nothing different between them.