Anyway, I got to reading and thinking about the importance of fire and water, and how they are so terribly important to the sacrifice, mostly because if we envision the sacrifice as a shared meal (which, of course, it is), then fire and water must be present: they are the two primary elements required to prepare a feast for someone.
Additionally, there are two different PIE roots for both these items: one that is gendered (and thus "animate") and one that is not gendered (and is thus "inanimate"). I made this nifty table in my head for the two different types of fire and water (with a third column to describe the gender of the animate types), and thought others might find the table a bit useful, too.
So, why two different types of fire and water? Because while "all Waters are by their very nature sacred," not all "water" is: brackish, undrinkable or poisoned water isn't sacred nor is it fit for ritual use. It is the same with fires: specific fires that do specific things may very well not be sacred. You would not, for instance, consider a trash-burning fire sacred. This is why you never, ever burn anything except fuel and offerings in a sacred fire. Placing cigarette butts or other refuse in a sacred fire is offensive to the deities, because the fire consumes, transforms, and provides the offerings it has received to the deities in the form of food or gift.
These active, living flames and waters are purity and truth. The fire burns those who are not pure or truthful, and the waters do not tolerate those who lie or go are impure. When offerings are placed within them (food laid upon the fire, drink poured out in libation to join the waters), fire and water are the messengers to the deities of not only what is given, but the intention and the person behind it, as well.
Next up? Of Gods and Humans: A Comparison