While working in 3d last year I discovered this optical illusion.

A large grid seen rotating at a certain speed will appear to group itself into smaller grids, spinning independently.

In this example, we see a central grid, and 3 or 4 orbiting it.

Here there appear to be about 5 or 6 grids:

at a lower frame-rate it looks almost like liquid.

It appears the persistence of vision effect overrides our knowledge that this is a single grid and divides it up optically. This only seems to work on a uniform grid (I also had interesting results with a brick formation), but the effect is lost when using a checkered texture.

© D.M. OReilly et al