Uguisubari (nightingale (flooring), method of laying floors to deliberately make a noise (like a nig (鶯張り)
Uguisubari is a corridor used for warning that the enemy has entered. When walked upon, the floors creak and make a sound.
In ancient Japanese architecture, some floors were designed to creak when walked upon so that the danger of outside intruders was detected, the mechanism was called uguisubari. In addition to a noise on floors, walls and architecture were also designed to make a sound. Such constructions that produce similar effects with simple mechanism include clappers as well as gravel and pebbles spread all over the garden.
There are several theories about the origin of uguisubari, including one that uguisubari was intentionally designed or it naturally occurred. As the design technique has not been handed down, it is said that producing the same kind of floor is now almost impossible.
As uguisubari was designed so that weight can cause the floor to make a sound regardless of the way of walking, there were many limitations in daily use. Therefore, in some cases, it was decided to walk down the corridor in a certain rhythm so that a person can tell an outsider from an insider by listening to the sound.
In English, uguisubari is called nightingale floors or singing floors.
In general careful constructions, for fixing floor joists to floorboards, nails are driven to the floor joist from the top of the board in a way that one end of a clamp is nailed to the side of the board and another end is nailed to the floor joist so that the nailheads cannot be seen. On the other hand, in the case of uguisubari, as the floorboard is wide, both ends of the board are curved upward a little and further, holes of the clamp nailed to the board are designed to have a clearance in a degree to allow the floorboard to move up and down when the floorboard is not curved. Therefore, when the top of the floorboard is stepped on, the floorboard returns to the non-recurved state, by which one end of the clamp rubs against the holes of the board, and makes a noise.