Once upon about 20 years ago, in a small, independently-owned upscale toy store, I saw a set of children's wooden blocks for sale.
It isn't going to help that I can't recall the exact name under which these blocks were marketed -- it was something along the lines of Wonder Blocks or Impossi-blocks, if my memory isn't failing me completely.
For the most part, they looked exactly like standard pine rectangular-solid blocks, other than some symbols that were wood-burned onto one face of some of the individual blocks. Those particular blocks were altered in one way or another: some had one end heavily weighted; others were simply hollowed-out shells and thus quite lightweight in comparison to the other blocks in the set; there were other variations, but I don't recall the details.
These alterations led to the ability to create what appeared to be gravity-defying structures.
Any ideas, oh LJ? Oh, and please feel free to pass the question along to anyone you know who might know (but if you would, link back here so the answer eventually gets to me?).