Alien Acrylic Art 2

Here is my younger brother with his finished artwork.
He was born with Down Syndrome. He has always liked to draw and paint (especially spaceships and outer space themed pictures, which is why we bought this kit for him).
Since he has developed hand tremors, I helped by painting the buildings. Can you see my flaw? I didn't notice it till we had driven him home and they were hanging it on the wall. Where's Fix-It Felix when I need him?