The 'rr' - the trill - is unequivocally the most difficult sound for me to make. All of the other Na'vi sounds I have no trouble with.

I did manage to 'get' the very beginnings of it a day ago, and progress is a little slow.
I'm practicing mainly by repeating 'vrrtep', 'krr' (sometimes helps to use 'lekrr' instead), and larger phrases including them (I'm particularly fond of "Nga lu levrrtep, ma oeyä tsmuke": My sister, you are demonic). Also 'burrito'

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