I found this delightful animation today:
The ball is traveling around a shape that can’t exist in our real world: the Penrose triangle. This illusion is the basis for some cool art, like Escher’s Waterfall. And I’m using it in my Math You Can Play books as a design on the back of my playing cards:
Want to Play Around with the Penrose Triangle?
Here’s a few links so you can try it for yourself:
- How to Draw an Impossible Triangle
- Build a Penrose Triangle with Legos
- How the Lego Triangle Works (Impossible triangle in Perth, Australia)
- Or Make a Paper Model
- How I Made the Image for My Playing Cards
Book Update
I’ve sent the first two Math You Can Play books to a copy editor (she edits the text part), so my focus this month is on finishing the illustrations and downloadable game boards. And designing the book covers — I think I’ll call this latest iteration done.
If everything stays on schedule, both Counting & Number Bonds and Addition & Subtraction should be available by mid- to late-spring. Fingers crossed…
Denise Gaskins' Let's Play Math 
Hint: If you are trying to build the Lego triangle, don’t use the yellow one above as a guide. I’m pretty sure that one is Photoshopped. Instead, look carefully at the red one after the cartoon here — a tricky change in a few small bricks makes the illusion work.