This morning I watched a few episodes of the British TV show QI, a a sort of comedy quiz show hosted by Stephen Fry. One of the questions was about how many steps a person can take before definitely spilling a cup of coffee. The answer is between 7 and 10 steps. It is predictable like that because of the physics of liquid oscillation. The liquid in your cup starts moving, and as you take each step, the ripples in the cup build on themselves so that no matter how smoothly and carefully you walk, eventually you are going to spill some.
I was thinking that this would be a good way for disabled people to measure just how off-kilter our walking is ... if weird walking is part of our thing ... or how skilled our handling of a wheelchair is I suppose. Judging from the blotches of tea on the tile floor of my kitchen, I can go at most 3 steps before I start slopping.
On "QI", after Fry explained how oscillation works, he talked about how it might be possible to invent a cup that counteracts oscillation so it would be spill-resistant. I literally did not understand the explanation, but I would buy the hell out that cup.