This one reminded me of arteries and veins crisscrossing their way through an organism.
The wallpaper version is available at the preceding link.
Today's Gratitude Item: That my students only broke one test tube in our lab today - they are a group who find Science challenging and are sometimes not as careful as they should be. They do love doing labwork though - this is why teaching Science is a lot "easier" than teaching Maths. Its way more prep though!