Their voices.

One thing I wonder is just how the voices of the Avatars would sound to the humans, and vice versa, in the movie the voices are the same( and that makes sence to do, but I wonder if they wouldn't sound a bit different in the "real situation") I wonder if, ( lets say you had two friends that both had Avatars, I wonder if when they are both driving avatars thier voices "sound the same to them" even though I would tend to think the voices would be a bit deeper due to size. But if one was walking out as a human and the other was an avatar then the human friend would notice the deeper sound in his friends voice, and his friend would notice that his human buddy sounds a little higher pitched to him, IDK, just something that came across my mind :)

Good Point man :)

Altough my opinion is, I often like to think of these things anyway, not regarding Avatar but just Humans. And I may be wrong, but from my experience I found that Voice is a very peculiar and Unique feature, and size, or atleast let's say Height in this case and generally slim people, I notice it's very Unpredictable wether it'll be deeper or higher pitched or louder or not. Some small dude may have a very deep voice and viceversa a very tall dude may have a very soft one.

Therefore I think, generally due to the considerable height related to humans, there could definitely be a general deeper or stronger appeal to their voice, but not so huge a difference In my opinion.

^ that is very true, and to an outside observer they may not even notice. Now if they are really good buddies and are used to chatting with each other they may notice the difference between them and find it interesting :) Irayo for your thought on the subject tsmukan!!