There's a color version of this at FredArt.
Part of writing involves knowing what happens even when you dont show it in the comic. Eventful and non-eventful things happen, often never really known or mentioned, or sometimes refered too in the future. You simply cant follow everyone through every scene right thru to them getting home, brishing thier teeth then going to bed - tho MT gets pretty close to showing that. This drawing is just a snapshot of such a scene, pretty much right from one of the lines in my notes today about 'where did we leave Yuki and Ping), etc.