C figured out how to open the sliding cover of our couch's center console. My husband used to hide things in there (remotes, game controllers, things we would confiscate from him, etc.). But now, no space is sacred!
It was funny when he realized he could slide it open, because he did it accidentally the first time. My husband tried to stealthily hold it closed after the first time, to psyche him out - but it didn't work. He's too clever and cannot be bamboozled. He just kept prying on it, would give up for a few minutes, then return to it to try again, until finally he came when Dad wasn't there. And quickly realized that it was no accident when he opened it, that he had conducted this momentous action on his very own!
He checks back with it every day to make sure he can still open it - just checking!