Aha... I get it. Wrap the square around a cylinder, and the diagonals will make a spiral. Project that spiral onto a plane, and you get a trig function. Clever...
Animating it isn't terribly complicated, once you get the square wrapped around the cylinder... that's a little bit tough for an amateur like me, but I imagine it could be nicely done using morph targets, or even bones. I just might give it a try....
The video you linked was very nice too, excellent explanation! Although, I'd be very interested if such a thing existed for Fourier transformation... I never could wrap my head around that one. Quaternion rotations are also a bit confusing. Well, going between them and Euler rotations, anyway. Then again, Calc For Business is the extent of my math schooling so.... <_< ;;