This is a one-shot of what I think was going through Sully's head when he unintentionally scared Boo in the movie.

Enjoy!

Sully was brought out of his roar when a little someone cried with horror at the creature in front of her. Out of the corner of his vision she watched her sprint quickly away from the monster.

"Boo?" He called back to her, his voice slightly trembling as she ran away from him.

He slowly followed her behind a set of simulator ramparts, which leaned idly against a wall. He rounded them slowly, spotting her pressed up hard against the wall, as if wishing to somehow sink into it if it allowed her to get as far away from him as was possible. Her eyes on him sparkled, growing misty with frightened tears as he approached. "Boo?" He repeated getting to his knees to reach his paw out to her, mindful to use all the care and gentleness he had to muster so he wouldn't spook her.

But that hardly mattered, as she carefully got back to her feet and slipped through a gap made by one of the artificial walls, maneuvering herself so that she would avoid Sulley's outstretched hand.

"Boo?" Sulley said yet again, hurt and stunned that she refused to come anywhere near him.

He looked towards the only other exit she could take through the makeshift tunnel and spotted her looking cautiously around towards him.

He tried to console her with more words, convincing her that he would never hurt her. "Boo it's me." –Kitty, was the unspoken part of that sentence.

But she just ran away again, backing up so she could see him coming closer so he wouldn't try and get her from behind. But her awkwardness cost her when she tripped suddenly on a loose cord and tumbled to her rear, just so her hood could fall off when she sat back up.

"The child!" Waternoose cried with surprise as he turned just in time to see her clear and terrified human face.

Sulley heard Mike explain the situation to their boss, quickly and carefully, making sure he left nothing out. Sulley's whole attention though, was entirely focused on the little girl in front of him. He got once more to his knees, desperate now to show her that he wasn't someone she needed to be scared of. "Boo? No, no, no, it's okay." he said once more, reaching his paw out like he did before. "I was just—,"

But his action terrified her, drawing the tears from her eyes and making her ball up to shrink into her costume for protection from the monster in front of her.

His heart broke by that and he retracted his paw, seeing now that it did nothing but frighten her worse. "Oh no. No, no, no. Don't be scared." He whispered, trying desperately to make her understand. "That wasn't real! It's just a… I was just…"

But then his eyes drifted up to the screens in front of him. The cameras catching the pictures had all been strategically placed so trainees were able to view all the different angles of the room while they scared the simulated child in the bed.

Sulley never once felt any regret for his job. Scaring was a way of life that all monsters were part of, and he loved every second of it. It was everything he had ever wanted to be. But he never once gave any consideration to how his scaring was taken on the receiving end of a little child. Humans had always and forever been nothing but creatures of energy for their world. They weren't people, not really, or at least not to monsters. Scaring was never personal, it was all business.

Yet looking up at his face, twisted and flexed into a hideous creature, crafted entirely to haunt a child for years and years, a new sudden doubt grew into him. It grew even more when right beside his face was a screen that had captured Boo's expression, caught in all her terror of him. And now here she was, bent and cowering right before him… as if he were… as if he were…

…Randal!

Did all children feel this way, right after being terrified to their core? Did they feel helpless and alone? How many sleepless nights did they suffer from because of the monsters in their closets?

Having Boo around, short time though it was, had been an enormous wake up call. She hadn't gone to sleep easily the night before and had stressed her fears of Randal with every chance he showed up. And now that same fear was painted over her face, only now she was afraid of him… Sulley… her kitty.

Images of familiar children, whom he had scared before, flashed through his mind, clear and focused as if they were right in front of him. He saw their torment, their fear, but most of all, their helplessness. But in each face, he saw Boo, just as she was in front of him now.

At that moment, Sulley realized he would never be able to scare another child again.

He looked back down to her, wondering how she would ever forgive him for this. "Boo…"

But as he watched her get suddenly up and rush to the side of Waternoose for protection from him, Sulley realized she would never be able to. And what was worse, was that he couldn't blame her.