Coxeter and Boerdijk noticed that you can stick regular tetrahedra together to make a spiral. Interestingly it never repeats: no two tetrahedra have the same orientation in space!
Click on the link to watch a short animation of it - it's fun!
en.wikipedia.org/wiki/Boerdij...
Click on the link to watch a short animation of it - it's fun!
en.wikipedia.org/wiki/Boerdij...
