"The Sensitive plant (Mimosa pudica L.) is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched, re-opening within minutes. Mimosa pudica is native to Brazil, but is now a pantropical weed. Other names given to this curious plant are Humble plant, TickleMe plant, Shame plant, Sleeping Grass, Prayer plant, Touch-me-not, Makahiya (Philippines, meaning 'shy'), Mori Vivi (West Indies), mate-loi (false death) (Tonga) ...

... In the evening the leaflets will fold together and the whole leaf droops downward. It then re-opens at sunrise ..." (Wikipedia)

We know (e.g. from the myth about Ulu and Mokuola) that life and death are two sides of the same coin - unless somebody dies life is doomed. The act of sacrificing good specimens will generate strength in those who live on. The 'vital spirit' is so to say transferred to a new body.

To sacrifice or to be willingly sacrificed is important in difficult times. And difficult times can be avoided if people sacrifice as a precaution. And a hanging 'fish' is like a mimosa plant, death is not definite but only illusory, because life will recycle into a new vessel.

Rau means 'leaves', 'to multiply', etc, and hei is 'head-band', 'to entwine', etc. Taken together rau hei can then be understood as 'proliferate from being entwined with a string of heads' (of hanging sacrifices, with their heads like beads on a pearl necklace).

The concept of being connected with invisible cords to the dead was a prominent feature of the beliefs of the ancient Polynesians.