Saka Men

Shinto monks believe the Shimenawa rope represents the border between the lands of the physical and those of the spiritual, and the rope is often put up to indicate that a location is taboo and the rope line shouldn't be crossed by the living.

Those mortals foolish enough to ignore this warning may find themselves faced with unspeakable horrors from the spirit realm, where human flesh is but a plaything

(Source: neatorama.com)