Probably the silliest and certainly the most difficult dexterity puzzle in our collection is “COSMOLINK” by Soft Space Inc. of California. It is a 70mm water-filled sphere on a stand. (Unfortunately it may now be even more difficult than when new, as some water has been lost in the last 30 years).
In the water there are lots of tiny (0.7 mm) neutral buoyancy balls coloured red, blue, and yellow.
The instruction manual of 8 small pages is very useful. It describes how to prepare yourself for a properly meditative state. When ready you focus on one ball and with the power of your mind move it. Once you have mastered this you concentrate on a group of balls.
If you are really good you can sort them all into their colors using only the power of you mind; and when you have really tuned into the “resources of your right hemisphere”, you can even apparently form letters and geometric shapes.
In 30 years we have never managed to do any of this, but as the manual helpfully says: -
adapted from CFF Magazine in 2008