Mirror Spock wasn't sure what to expect when he mind-melded with Dr. McCoy. It had been a bit of an impulsive action; he wanted information and a meld was the easiest way to get it.
Everything he saw in Bones' mind had a surprising quality of mercy to it – the doctor working hard to save people's lives and losing sleep over patients, inquiring interactions with other aliens – all of it tinged with kindness.
At first Mirror Spock was filled with disgust. Such displays of trust and graciousness were not logical. But then he felt a small amount of pity for those in the Empire, and victims of the Empire. "Live by the sword, die by the sword," may have been an efficient way to live, but it wasn't usually pleasant. The only person that he ever felt that he could trust was Kirk.
Well, he wasn't even really sure of that, sometimes.
He left the mind-meld, and Bones saw, for a split second, the look of shock and sadness on Mirror Spock's face. He quickly recovered, however, and pulled the doctor along by the arm.
"Come along," he said. "It's time you went home."