A number of fascinating superstitions have made their way through Japanese culture. Below are a few that intrigue:
Hide your thumbs when you see a funeral hearse
This is a superstition that came about through the wonder of the Japanese language.
In Japanese, the word for parents is oya (親). To make sure our parents don’t meet the same fate as the poor soul in the funeral hearse, we are supposed to hide our thumbs or oyayubi (親指) when we see a funeral hearse drive by. It makes wonderful sense.
Don’t pass food from one set of chopsticks to another
The reason for this seems to come from a unique Buddhist ritual that takes place during cremation ceremonies. In this observance, the bones left over after a cremation are carefully placed into an urn, requiring them to be passed from one set of chopsticks to another.
There appears to be significance behind the use of chopsticks, too, and this again is a play on the Japanese language.
Chopsticks and bridge are both known as hashi in Japanese (albeit with completely different characters: 箸 and 橋), and in order to cross from this world to the next, the deceased must cross a bridge. Seemingly, the use of chopsticks in the ceremony makes the crossing easier for everyone involved.
Don’t clip your nails at night
There looks to be a few hypotheses as to how this one came about and the first is again a play on words. Night and nails can be written as yozume (夜爪); another way to write yozume, however, (this seems to me to be a bit forced) is to put the two kanji for world or life (世), and shorten (詰める) together to make 世詰.
The second theory comes from pre-electricity Japan when it was, by all accounts, almost impossible to cut your nails safely at night under the blanket of darkness. Without modern day nail clippers, armed only with a pocket knife or perhaps some scissors, accidents and injuries happened. The accidents were so severe in fact that they prevented the injured from working, thus affecting the household’s income, and in turn leading the proprietor to an early grave.
Don't step on the edge or border cloth of a tatami mat
Three or four theories follow this one, but considering the previous three have had mildly dark undertones, I've gone with one which is perhaps the most fun.
One theory has it that by avoiding stepping (or sitting) on the cloth-edge of a tatami mat, we are in fact keeping ourselves from harm. From ninja.
The Sengoku period, which lasted until the early 1600s, was a period of constant military conflict between and within different regions of Japan. It was during this time that ninja were active as, amongst other roles, assassins. An apparent assassination technique of theirs involved getting under the flooring, and using the sliver of light seeping through the edge of the tatami mat as a marker to where their target might have been.
Once the ninja had his victim in sight, he would thrust a blade up through the small gap, and exterminate his target.