Don't do this in Japan ~5~ Tatamiberi

Have you seen the Japanese styled room?
We often see Japanese styled room like this in each house.

The mats on the floor are called "tatami". You may have heard of that.
The mat is made from a rush.
This is Japanese traditional mat. In Japan, we see a lot of westernized house
in the city. But many Japanese people still like the tatami room because
they feel comfortable. Japanese people sit on the tatami floor.
On wikipedia, I learn that the origin goes back more than 1200 years ago.
In Japan, we express the area of room by the numbers of tatami.
For example, we say "this room is 7 jou." (jou is the unit)
It means, you can lay out 7 number of tatami in a room.
The size of tatami is always same in Japan. So, we can guess how large is the
room.

I've got interesting story.
In Japan, it is said that people should not step on the tatamiberi.
(Tatamiberi is the edge of each tatami. Do you see the green color edge?)

I have heard that when I was kid. I heard that it is inauspicious.
But why?
I have heard that ninja used to hide under the tatami in the period of samurai(more than
400 years ago). And ninja used to assassinate a person by stabbing the part of tatamiberi.
So someone say that.

Tatamiberi is damaged easily and worn easily. So, you should take care when
you have chance to get in Japanese stylish house.