This box opens with only one move. The cover rattles. But, the cover doesn'topen even when you pull it up or turn any points of the box. It was unveiledat an exhibition that was held in Feb. 2008 by the craftsman and Mr.Ninomiya. At the exhibition, a customer who experienced Karakuri for thefirst time opened it very quickly, but a veteran of puzzles needed 30minutes. This caused a lot of laughter! The acorn is made of wood. This workwas designed for the marriage party of the craftsman's friend. RF-20-1 is acommercial version of it.