So I found a book about Avatar by coincidence at one of those discount book disposal stores this weekend.
And it explains Navi culture and the flora and fauna (so I will post names with pics at some point for the stuff found in the land).
The part that interests me is the vision hunt - sort of like a vision quest where they go in search of their spirit animal and it's a right of passage leading up to the banshee riding thing.
Well, in the River Journey you see the two animals required for the vision hunt (both produce a type of hallucinogen - the glow worm in the caves at the start and the millipede liking thing on the screen rock arch). It also features the hexapede which is the first animal a young Navi is allowed to kill on their way to adulthood and the eventual Ikran/banshee right of passage.
The book also describes their music and their hunt songs and the sort of songs from a vision hunt as well - which very much suggests that the River Journey is like your own metaphorical vision hunt before you get to the triumphant Ikran bonding.