Sometimes it's the tiniest things that remind him that he's different.
Like Chloe, squinting against sunlight and later rubbing her eye, griping about seeing white spots. His retinas will never burn; he'll never experience that.
He worries about those things, the tiny bits of scattered evidence of normalcy and humanity, worries about what they mean for him and how they'll expose him one day. Whatever story he concocts, whatever lies he invents to always pass himself off, he'll never get it just right.
Which he knows. Once, in sixth grade, his English teacher had told them all to write a story, and she said, "Write what you know. It'll be best that way." Clark knew about younger days, stretched on his belly next to a corn stalk and wondering if he could see it grow, if he just didn't blink, didn't move, didn't get distracted by anything. He knew about dirt caked under his fingernails so deeply he was glad to feel no pain when he used a pocketknife to dig it out. He knew about the lines on his mother's face that hadn't been there in the past, and about the shadow of worry on his parents' faces when they sat down to pay bills.
He didn't think any of that would make an interesting story. He wrote it anyway; he thought maybe it was good practice for the rest of his life, to take what he knew of living a human life and make it convincing. Make it fiction worthy of the world.
But the problem now is that every day someone wants a more complicated story, a story to fill in every gap. Lex looks at him and challenges it all, tries to find the holes and rip Clark's words apart, and every day it gets harder to deny the truth. He lacks the details, the knowledge and experience of how bones shatter against a car fender and how to save someone when you can't rip doors and roofs off. Of how bruises feel after getting tackled in football. Of just being allowed to play at all, no questions, no concerns.
Sometimes, Clark is sure that someone will figure it out. Because there are just too many of those little things to account for.
He's never been very good at writing, anyway. His story got a C.