Tetrahedron packing

Imagine you have a bunch of little toys that are shaped like triangles. When you try to put them all together to make a bigger shape, like a cube, they don't fit perfectly together.

But if you use toys that are shaped like four-sided pyramids (also called "tetrahedrons"), you can actually fit them together really nicely to make bigger shapes.

It's kind of like how when you build with blocks, some blocks fit together better than others. Tetrahedrons are like the blocks that fit together really well.

Scientists use this idea of how tetrahedrons fit together to study things like how molecules fit together in different substances. It's like a big puzzle!