"Nothing, just my imagination," he dismissed it as just being exhausted. Plus, it wasn't as if he knew it was fake. The smile just looked fake.
Regulus just laughed. "Kreacher's smarter than that, he'd use a regular size knife to try to throw the suspicion off of himself." He'd actually just try to push her down the stairs and make it look like an accident but he wasn't about to tell her that bit of it.
"The elf will behave himself but I have no control over the portrait."