The Hanayama Cast Rattle puzzle is a design from Bram Cohen.
There are four pieces that make up the puzzle which are loosely interlocked. The aim is to try and seperate the pieces and then reassemble.
A challenging little puzzle it seems like it should be easy at first but there are very little clues as to how to go about it.
This is rated 5 out of 6 on the Hanayama difficulty scale.