Billy and Harley's relationship is pretty clear to me by now. Billy won't do anything if Harley tells him to. He can be seen outside a lot having fun by himself, but if Harley makes him go outside, he'll make it a living nightmare for him. Despite this, Harley will always keep trying to make him do what he wants.
This strip is set on a staircase, which might be weird because I've never really shown a staircase in the strip before. But I actually have, once, in this old and very bad Billy strip. I like to carry things over in the strip, even if they're tiny things no one in their right mind would notice. Drawing this made me want to set more strips on that staircase.