A disentanglement puzzle invented by Anneke Treep & Christian Freeling. Called Teaser Balls on PuzzleWorld.
The Starting position:
Loosen the left side of the square knot, forming a loop which is pulled over the black ball. As an ALTERNATE first step, the diagram below can also be reached by pulling a loop from the left side of the square knot and threading the pink ball under it! Using this alternate technique no ropes will pass around the black ball. However, it is more difficult to remember how to reverse the steps.
Continue pulling this loop upward, through the fixed loop from the black ball.
The solution should now be obvious. Enlarge the loop sufficiently so that the pink ball can be passed through it.
And then simply pull the loop through the fixed loop.
The balls are now untangled. To reset, reverse the solution steps for the next victim.