What do the Na'vi use their tails for?
 

Besides stability?:)

to add to their sexiness :love:

According to the Pandorapedia, some types of Na'vi are able to hang from their tails. But mostly, I suspect the tails are balance (part of the original form, and still very useful I imagine) and also (either consciously or not) as part of how they express themselves emotionally.

^That's the thing, though. When I read that they use their tails to climb and hang and whatnot, I was thinking about what I had seen in the film... and I never saw any Na'vi do anything with their tails but wag 'em.

That's because the Omaticaya can't do it, apparently.

^ that <3

And well i have few ideas for what they can :airquote:use it:airquote: :awesome:, but i can't write them here :)

To making a mess. :P
http://img840.imageshack.us/img840/9194/47934175.jpg

*melts*:awesome:

It really is possible that something as minor as adding to their sexiness could be part of it. If the Na'vi see having a healthy expressive tail of a good length as being a desirable quality in a mate then over many generations sexual selection pressures would prevent them from dwindling even if they served no practical function.

this :love:

Balance, good looks, emotional display...
That's my guess.

But I think tm20 has the best answer. :)

This.

There are tons of animals that do this already. Gorillas like the silver fur that grows on the backs of the males, Anole lizards are more attracted to male anoles that have a larger or more colorful dewlap, and bowerbirds actually build things to attract the female's attention, but none of these things actually benefit the animal physiologically. They only exist as a means of sexual selection, and they generate pressures on the genetics of the population that drive whatever direction the population is going in, in evolutionary terms.

maybe for balancing, like cats

Expression. Some of the Na'vi tail movements really draw the eye to them, and it's a part of their body language. A tail can, as has been suggested, be part of attraction as well.
Of course, we all know tm20's answer is true :)

I'm not going for the whole prehensile tail thing unless it appears in a film or source like the survival guide (I suppose it could be possible that all Na'vi have the ability but some have just not learned to, but it doesn't visibly seem to have that much strength) since that would mean they are a different species (and the pandorapedia is not an accurate source, it also says some Na'vi have other extreme physical differences, which would be unlikely).

I kinda like it, myself. In humans, we do actually have differences depending on where we live - pale skin in northerners to catch more sun (possibly particularly in women, as I read somewhere women tend to be a couple degrees paler than men, no matter what their ethnic group is like, so she can absorb more vitamin D for any growing baby), widely different shaped noses, the Inuit and some Siberian groups actually give off more heat than other types of human as part of their adaption to the cold, and so on and so forth. And you just have to look at dogs to see how widely body plans and abilities can be within the one species. My old kelpie/border collie cross was very different from my current rhodesian ridgeback/lab cross, both in their bodies and in their instincts. And wolves and dogs can still breed, but they, too, are EXCEEDINGLY different, particularly in instincts.

And, well, the Pandorapedia was on the blu-ray, so it's more legit than most - although, yes, still optional canon.

Interbeeding of wolves and dogs isn't that comparable - dogs are closely related to wolves, although domesticated ones have been selectively bred for many, many generations, the selective pressures have been mostly in attributes such as size and temperament (hence why interbreeding is difficult, but not impossible), while humans have evolved beyond the stage of interbreedability with other primates. Dogs that live in the wild (not feral dogs, although they may be to a degree) are more similar to wolves in instinct.
Na'vi having a completely different tail structure and musculature would be equivalent to some humans having six limbs. It's not likely for them to end up coexisting as one would get selected for over the other barring extreme geographical isolation, particularly if the extra features do not confer an advantage in survival, and if they did both exist, they would be considered separate species. I'm not saying it is impossible, but it seems extremely unlikely, as well as the simple fact that suddenly revealing that with no reference anywhere beforehand would be extremely bad planning and design, and Pandora seems far better realised than that.