I remember reading about Hinton's cubes in an old Mathematical Games anthology,
so a cumulative index would be the thing. Gardner wrote about them and
apparantly they worked, but there were stern warnings not to play with them,
because (!) they cause insanity in some people(!!). Gardner said something
to the tune of that the human brain is not meant to do 4-dimensional geometry,
and these things will make your brain bugcheck. Ever since then, I have been
fascenated by the thought of a puzzle that would blow your mind literally! Of
course, this was in the days before it was fashionable to use chemical means
to do this. Anyone else know anything about them?

Jon