Hey, want to make your brain hurt? For inexplicable reasons, the subject of quantum entanglement came up at work. Someone pointed me at a paper that explains certain aspects of the phenomenon, because I mentioned that I had thought entanglement was a binary situation - a pair of particles are either entangled or not. But it turns out that there's such a thing as partial entanglement, and multiple particles can be entangled. I'm not going to pretend to understand this fully, and the math completely defeats me, but I think I grasped enough of it to say "ow, my brain." And to appreciate that, while the rules underlying reality may ultimately be fairly simple, they can give rise to a near-infinite complexity.