I was constructing a visualization of US external debt, when I noticed something interesting: the amount of US debt owned by China and the UK seem to be anticorrelated. More specifically, whenever China purchases a large amount of US debt, the UK sells off a similar amount; whenever China sells US debt, the UK makes a purchase. One such documented example: in 2010 China sold off $34 billion in US government bonds, which was met with the UK buying $24.9 billion of US government debt. I'm not sure if this is meaningful or merely attributable to simple market forces. Perhaps the US has asked the UK to help out in this regard to avoid large fluctuations in total US debt. Meaningful or not though I thought it was noteworthy, and a good example of how data visualization can help us discover things we otherwise wouldn't have found.