Years ago, I painted the hall with chalkboard paint, and sometimes stuff appears there that I take a picture of before it's gone forever.
The large rectangle was drawn by Cookie. You can't really see that there are pink squiggles in the center. She told me, "It's a magnified view of the bloodstream. The white blood cells are eating the germs." It's funny to hear a 6-year-old describe something like this, especially when she still pronounces it "bwood."
Then Princess added the sick boy cutaway, showing organs inside him and various ailments. He's taking a pill that is half blue, half white, which is labeled "medicine" in the accompanying key. There seemed to be a chain of events, not visible in this small picture, that reads: "large intesting --> white blood cells + cough --> poison ivy + small intesting --> fever --> germs --> medicine." I'll wait awhile before I bring up the "intesting vs. intestine" issue. No need to jump on it too eagerly.
The cartoon face was Gameboy's contribution; it's Albert Einstein. I think it annoyed the girls that he drew it there, but it's all gone now anyway, making room for other stuff.