How is a NaN created?

The following practices may cause NaNs:

* All mathematical operations with a NaN as at least one operand
* The divisions 0/0, 8/8, 8/-8, -8/8, and -8/-8

However, it is important to realize that these NaNs are not necessarily generated by the processor.

now I had a NaN and it fugged up my whole world
we were using a shader that we had never used before
every time we rendered the plates, and I am talking 1 gig plates,
black spots would show up on the surface
i looked at the logging statements on the farm
and whaddya know…NaN