Think of it as being in a 5/5 time signature... more info in the "story behind the song" and there's a video that helps as well.
Story behind the song
What if instead of our rhythmic obsession with threes and fours we used ONLY rhythms of five? Imagine an isolated island that evolved their music's rhythms based purely on the fingers of one hand.
If that happened, you might get musical sections that are five or ten bars long instead of our usual four or eight. Each bar would have 5 beats, like we sometimes do but for them it would be "normal" instead of odd. Those beats would be divided into 5-tuples instead of eights and sixteenths, and occasionally the percussionist will throw in a nested 5-tuple inside the 5-tuple as a blindingly fast flourish. Maybe they'd be comfortable with 5-tuples that encompassed two beats; their version of a triplet.
We'd likely call it 5/5 time, but if you want to see what the rhythms look like in our standard 5/4 notation there's a picture of it in the Dollar Bill photo gallery.
Bill played 12-string guitar, wind wand, zils, rain stick, and claves.
Lyrics
(Rongorongo is a dead written language that no one seems to be able to translate.)