Presumably the origin of the system is the Cat's Cradle patterns (kaikai), where a string without ends is the instrument for exhibiting the moving figures.

When a glyph is 'open', i.e. the 'string' has ends (the contour line is broken), the glyph carries a message: 'not of this world' ('supernatural').

The principle of 'openness' meaning a being from the 'spirit world' is found not only in the rongorongo system, but also elsewhere in Polynesia and among the Indian cultures of South America:

"Figs. a, b and e are Peruvian spirit emblems painted or embroidered on the burial gifts formed like sails ... Figs. c and d are petroglyphs of a type common in the Marquesas and Society Islands ... This peculiar type of Polynesian petroglyph represent, like so many of the Peruvian spirit emblems, an anthropomorphic figure drawn in two parallel lines in such a way that the body is not joined at the hips. Fig. f is a petroglyph from Kauai, Hawaii, reproduced by Bennett ... who describes it as 'triangular body not joined at the hips.' He further says ... of the local anthropomorphic figures in Kauai petroglyphs: 'Two, three, and four toes are found, with three as typical.' Both the triangular body, gaping hips, crooked arms, and a strange number of toes and fingers agree remarkably well with spirit emblems in early Peru ..." (Heyerdahl 6)

The Eskimo (Inuit) peoples have myths about the 'Entrail Snatcher', in which a bottomless body (bereaved of its entrails) indicates an 'empty shell' (dead person, spirit).