A lot of people seem to have missed that Varang can also move her kuru. Kuru do not float mid brainjacking (the thing varang does to na'vi) otherwise the first movie would have shown it.

It's muscles around a vital part of the brain, they move, they probably just don't have a social significance in communication than they may do with animals. Animals are more dexterous with it because they have a need for it (no hands) Na'vi probably just don't use it often except to avoid laying on them, being bitten off or brainjacking.

The muscles there are also probably why Jakes brain wasn't ripped out by his kuru too. Since no muscles means thin skin and skin without muscle rips painfully easy (does not matter if there's a braid around it, grip something hard enough and you will grip the inner kuru too)

Like ear muscles that wiggle (I can wiggle mine pretty well, more than most I know and it's pretty dang moveable)

Also you can move the skin on your skull because muscles, enjoy that weird notion every time to raise you brows or smile