A/N: This was written for the post Adhesive Duck Deficiency drabblethon at Paradox, the Sheldon/Penny comm at LiveJournal. Therefore it contains spoilers for that episode.
Disclaimer: I own nothing related to this show except the DVDs. I'm just borrowing these characters for fun, not for profit. Suing me would be the very definition of a frivolous lawsuit.
Changes
He leaves Penny's apartment as soon as she falls asleep (which is almost immediately after their round of "Soft Kitty" ends). Part of him wants to stay, and that's why he leaves, fleeing as quickly but as quietly as he can back to his own room, his sanctuary.
He tries to sleep, but it's no use. His brain is in a hot dense state, filled with images and sensory memories (he thinks he can still smell her soap on his skin). But what's troubling him the most is the memory of singing with her. Something changed in that moment, and it terrifies him. Terrifies him more than change normally does, because this change is something he can't quantify or classify. All he can say is that prior to that moment, he and Penny were just friends.
But taking care of her, and singing his mother's song with her seems to have awoken something within himself that he'd thought he'd been successful at suppressing; a nurturing, protective instinct, and such warm feelings he feels almost feverish.
So when she comes into his apartment the next day to thank him, and he looks up from his computer where his work (abandoned without second thought last night) is waiting patiently, all he can say to her is "…Hello."