http://tokyobling.wordpress.com/2012/01/24/the-house-of-ogai-mori-and-soseki-natsume/
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http://mochida.cc/archives/tag/%E6%9D%91%E6%AD%A3
Shimenawa (標縄・注連縄・七五三縄, literally “enclosing rope”) are lengths of braided rice straw rope used for ritual purification in the Shinto religion.
A space bound by shimenawa often indicates a sacred or pure space, such as that of a Shinto shrine. Shimenawa are believed to act as a ward against evil spirits and are often set up at a ground-breaking ceremony before construction begins on a new building.
They are also used to mark trees that are believed to be inhabited by spirits called Kodama. Cutting down these trees is thought to bring misfortune.