Plus reviews of “Pop! Goes the Nursery Rhyme,” “The Watering Can” and “Girlatee.” ...

Shape A, B and C all have 4 sides and 4 corners, but can you see that Shape D has 5 sides and 5 corners. This is the odd one out. A shape with 5 sides and 5 corners is called a pentagon.

The rectangle is a wobbly, unstable shape. When you push the side, it flops into a slanted parallelogram. This happens without any of the rectangle's sides changing length.

This polytope is actually a truncated octahedron, a shape with 14 sides (six squares and eight regular hexagons). And truncated octahedra can create a space-filling tiling of 3-space.

In 2006, he and one of his colleagues discovered a shape called the gömböc, which has the unusual property of being “mono-monostatic” — it balances on just two points (one stable, the other unstable, ...