I'm not sure how well this joke renders non-visually, but here's an attempt!
The Things are in complete darkness, you can only see their eyes and their eyes are white lines on black. Slowly Thing 1's eyes fill up with white, so it looks a bit more normal. Thing 2 still looks like an inverse drawing and is surprised. Eventually Thing 2's eyes flip black and white coloring and look a bit more normal.
Thing 2: My eyes take a while to adjust to the light